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Projective space

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is the construction of the scheme of a projective space, and, more generally of any projective variety, by gluing together affine schemes. In the case of projective spaces, one can take for these affine schemes the affine schemes associated to the charts (affine spaces) of the above description of a
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in both directions. The image represents the projective line as a circle where antipodal points are identified, and shows the two homeomorphisms of a real line to the projective line; as antipodal points are identified, the image of each line is represented as an open half circle, which can be
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All finite fields of the same order are isomorphic, so, up to isomorphism, there is only one finite projective space for each dimension greater than or equal to three, over a given finite field. However, in dimension two there are non-Desarguesian planes. Up to isomorphism there are
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are the coordinates on the basis of any element of the corresponding equivalence class. These coordinates are commonly denoted , the colons and the brackets being used for distinguishing from usual coordinates, and emphasizing that this is an equivalence class, which is defined
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under the equivalence relation between vectors defined by "one vector is the product of the other by a nonzero scalar". In other words, this amounts to defining a projective space as the set of vector lines in which the zero vector has been removed.
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and denotes the equivalence classes of a vector under the defining identification of the respective projective spaces. Since members of the equivalence class differ by a scalar factor, and linear maps preserve scalar factors, this induced map is
2527: 2301: 1896:. The term "projective transformation" originated in these abstract constructions. These constructions divide into two classes that have been shown to be equivalent. A projective space may be constructed as the set of the lines of a 3147:
The last axiom eliminates reducible cases that can be written as a disjoint union of projective spaces together with 2-point lines joining any two points in distinct projective spaces. More abstractly, it can be defined as an
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finite projective planes of orders 2, 3, 4, ..., 10, respectively. The numbers beyond this are very difficult to calculate and are not determined except for some zero values due to the
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The structures defined by these axioms are more general than those obtained from the vector space construction given above. If the (projective) dimension is at least three then, by the
1756:, once the concept is translated into projective geometry's terms. Again this notion has an intuitive basis, such as railway tracks meeting at the horizon in a perspective drawing. See 2010: 1884:, which, etymologically, roughly means "similar drawing", dates from this time. At the end of the 19th century, formal definitions of projective spaces were introduced, which extended 2797: 1709:, projective geometry has a different setting, projective space, and a selective set of basic geometric concepts. The basic intuitions are that projective space has more points than 82:, having two different sorts of points, which must be considered separately in proofs. Therefore, other definitions are generally preferred. There are two classes of definitions. In 2188: 1065: 4143:
In algebraic geometry, this construction allows for greater flexibility in the construction of projective bundles. One would like to be able to associate a projective space to
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asserts that is not so in the case of real projective spaces of dimension at least two. Synonyms include projectivity, projective transformation, and projective collineation.
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As Pappus's theorem implies Desargues's theorem this eliminates the non-Desarguesian planes and also implies that the space is defined over a field (and not a division ring).
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onto its image, provided that the neighborhood is small enough for not containing any pair of antipodal points. This shows that a projective space is a manifold. A simple
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In this section, all projective spaces are real projective spaces of finite dimension. However everything applies to complex projective spaces, with slight modifications.
1920:); in this context, collineations are easier to define than homographies, and homographies are defined as specific collineations, thus called "projective collineations". 3203:. In dimension one, any set with at least three elements satisfies the axioms, so it is usual to assume additional structure for projective lines defined axiomatically. 854:
the multiplication by a non zero constant. That is, if are projective coordinates of a point, then are also projective coordinates of the same point, for any nonzero
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for the study of homographies. The alternative approach consists in defining the projective space through a set of axioms, which do not involve explicitly any field (
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from a changing perspective. One source for projective geometry was indeed the theory of perspective. Another difference from elementary geometry is the way in which
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Properties meaningful for projective geometry are respected by this new idea of transformation, which is more radical in its effects than can be expressed by a
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The topic of projective geometry is itself now divided into many research subtopics, two examples of which are projective algebraic geometry (the study of
2707:{\displaystyle \varphi _{i}^{-1}\left(\right)=\left({\frac {x_{0}}{x_{i}}},\dots ,{\widehat {\frac {x_{i}}{x_{i}}}},\dots ,{\frac {x_{n}}{x_{i}}}\right),} 4897: 3968:, it can be shown that any algebraic (not necessarily linear) automorphism must be linear, i.e., coming from a (linear) automorphism of the vector space 4388:, pp. 6–7). Pasch was concerned with real projective space and was attempting to introduce order, which is not a concern of the Veblen–Young axiom. 3210:, p. 231) gives such an extension due to Bachmann. To ensure that the dimension is at least two, replace the three point per line axiom above by: 3639: 2517:{\displaystyle {\begin{aligned}\mathbb {\varphi } _{i}:R^{n}&\to U_{i}\\(y_{0},\dots ,{\widehat {y_{i}}},\dots y_{n})&\mapsto ,\end{aligned}}} 1934:
are supposed to be true. A large part of the results remain true, or may be generalized to projective geometries for which these theorems do not hold.
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are primitive entities that are related by the incidence relation "a point is on a line" or "a line passes through a point", which is subject to the
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For sake of simplicity, unless otherwise stated, the projective spaces considered in this article are supposed to be defined over a (commutative)
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points if one consider complex points in the projective plane, and if one counts the points with their multiplicity. Another example is the
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is a projective subspace if and only if, given any two different points, it contains the whole projective line passing through these points.
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does not apply in projective geometry, because no measure of angles is invariant with respect to projective transformations, as is seen in
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If the six vertices of a hexagon lie alternately on two lines, the three points of intersection of pairs of opposite sides are collinear.
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complex roots. In the multivariate case, the consideration of complex zeros is also needed, but not sufficient: one must also consider
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While the ideas were available earlier, projective geometry was mainly a development of the 19th century. This included the theory of
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It is possible to avoid the troublesome cases in low dimensions by adding or modifying axioms that define a projective space.
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Homogeneous required in order that a zero remains a zero when the homogeneous coordinates are multiplied by a nonzero scalar.
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of the space is defined as one less than this common number. For finite projective spaces of dimension at least three,
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to the vector line passing through it. This function is continuous and surjective. The inverse image of every point of
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An important property of projective spaces and projective varieties is that the image of a projective variety under a
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is thus a projective space that is obtained by restricting to a linear subspace the equivalence relation that defines
3219: 1927: 1315:, an independent spanning set does not suffice for defining coordinates. One needs one more point, see next section. 4798: 4618: 2766:. In both lines, the intersection of the two charts is the set of nonzero real numbers, and the transition map is 4609:, translated from the 1977 French original by M. Cole and S. Levy, fourth printing of the 1987 English translation 4252: 4883: 4330: 4325: 4275: 2928: 1702: 3568:
is a finite set of points. In any finite projective space, each line contains the same number of points and the
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and is projectively independent (this results from the similar theorem for vector spaces). If the dimension of
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the defining polynomials, and removing the components that are contained in the hyperplane at infinity, by
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is an ordered set of points in a projective space that allows defining coordinates. More precisely, in an
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The projective space, being the "space" of all one-dimensional linear subspaces of a given vector space
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during the second half of 20th century, allows defining a generalization of algebraic varieties, called
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theory. There is a bijective correspondence between projective spaces and geomodular lattices, namely,
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if that is the largest number for which there is a strictly ascending chain of subspaces of this form:
1736:). The first issue for geometers is what kind of geometry is adequate for a novel situation. Unlike in 389:
in this plane consists of all projective points (which are lines) contained in a plane passing through
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This restriction allows the real and complex fields to be used (zero characteristic) but removes the
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The correct definition of the multiplicity if not easy and dates only from the middle of 20th century
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can be described more concretely. (We deal only with automorphisms preserving the base field 
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A projective space is itself a projective variety, being the set of zeros of the zero polynomial.
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with the corresponding projective point, one can thus say that the projective plane is the
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As outlined above, projective spaces were introduced for formalizing statements like "two
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modulo the matrices that are scalar multiples of the identity. (These matrices form the
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Dimension 2: There are at least 2 lines, and any two lines meet. A projective space for
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And, to ensure that the vector space is defined over a field that does not have even
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implies that the division ring over which the projective space is defined must be a
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of projective subspaces is a projective subspace. It follows that for every subset
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Historically, homographies (and projective spaces) have been introduced to study
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There is exactly one projective line that passes through two different points of
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of the space (the intersection of the axes in the figure); the projection plane (
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with the projection plane. Such an intersection exists if and only if the point
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intersect in exactly one point, and this point is at infinity if the lines are
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with 7 points and 7 lines. The smallest 3-dimensional projective spaces is
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A third equivalent definition is to define a projective space of dimension
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of a projective space, there is a smallest projective subspace containing
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is non-zero and in the null space. In this case one obtains a so-called
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is the study of geometric properties that are invariant with respect to
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is the field of real or complex numbers, a projective space is called a
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This definition of a projective space has the disadvantage of not being
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points on a line, so the two concepts of order coincide. Notationally,
3547: 3354:{\displaystyle \varnothing =X_{-1}\subset X_{0}\subset \cdots X_{n}=P.} 988: 204:, projective spaces play a fundamental role, being typical examples of 190: 32: 1669: 169:, as allowing simpler statements and simpler proofs. For example, in 1635:. They are only defined up to scaling with a common nonzero factor. 481:(vector subspaces of dimension one) in a vector space of dimension 337:
split in two disjoint subsets: the lines that are not contained in
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and are projective planes over division rings, but there are many
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Dimension 1 (exactly one line): All points lie on the unique line.
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for clarity) of the projective plane as the lines passing through
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The absence of space after the comma is common for this notation.
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identified with the projective line with a single point removed.
142:"being on the same vector line". As a vector line intersects the 1520:; this representation is unique up to the multiplication of all 1341:-dimensional projective space, a projective frame is a tuple of 4879: 1861:. In general, some collineations are not homographies, but the 897:, respectively. The complex projective line is also called the 3408:
Projective spaces admit an equivalent formulation in terms of
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of them are independent; that is, they are not contained in a
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is the space of flags, i.e., chains of linear subspaces of
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of the topology of a finite dimensional real vector space.
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with only one nonzero entry, equal to 1), and the image by
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are considered. Then, the central projection maps a point
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There exist four points, no three of which are collinear.
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where hats means that the corresponding term is missing.
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for the basics of projective geometry in two dimensions.
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All these definitions extend naturally to the case where
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Dimension at least 3: Two non-intersecting lines exist.
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induce mappings of the corresponding projective spaces
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of projective spaces, induced by an isomorphism of the
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are permitted that transform the extra points (called "
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Completion of the usual space with "points at infinity"
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in such a chain is said to have (geometric) dimension
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on this basis are all nonzero. By rescaling the first
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Projective geometry: from foundations to applications
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Mauro Biliotti, Vikram Jha, Norman L. Johnson (2001)
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Further information on finite projective planes:
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Dimension 0 (no lines): The space is a single point.
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if its span is not the span of any proper subset of
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is a projective space, which can be identified with
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Mathematically, the center of projection is a point
5145: 5081: 5019: 4973: 4913: 4234:(rather than only fields) yields, for example, the 4056:. The automorphisms of the complex projective line 3281:The geometric dimension of the space is said to be 2751:, that is of a projective line, there are only two 4706: 4647: 3353: 2942:is the set of points in a projective space, whose 2791: 2706: 2516: 2258: 2182: 2039:A (finite dimensional) projective space is compact 2004: 1059: 463:Affine space § Vector spaces as affine spaces 113:(that is, vector subspaces of dimension one) in a 1849:from which the projective spaces derive. It is a 235:". Such statements are suggested by the study of 4715:Ergebnisse der Mathematik und ihrer Grenzgebiete 4613:Beutelspacher, Albrecht; Rosenbaum, Ute (1998), 4410:and other planes that exhibit atypical behavior. 4274:Another generalization of projective spaces are 3543:Projective plane § Finite projective planes 2762:, which can each be identified to a copy of the 3588:, whose order (that is, number of elements) is 883:is one or two, a projective space of dimension 4675:, Toronto, Ont.: University of Toronto Press, 4079:When the construction above is applied to the 3260:, such that any line containing two points of 3218:To avoid the non-Desarguesian planes, include 2721:Manifold structure of the real projective line 410:defines a projective line which is called the 317:, in green on the figure) that passes through 4891: 4797:, Cambridge Studies in Advanced Mathematics, 3855:they differ by a scalar multiple, that is if 3188:that states which points lie on which lines. 3070:(the set of lines), satisfying these axioms: 3014:can be built by gluing together open sets of 158:, and a projective space of dimension 2 is a 8: 4504:Aufbau der Geometrie aus dem Spiegelsbegriff 2177: 2120: 4244:Patching projective spaces together yields 3773:; in this case the meaning of the class of 3490: 3388:and so on. If the full space has dimension 3006:, by gluing together smaller pieces called 2969:with respect to the homogenizing variable. 2923:that allows computing the genus of a plane 2903:asserts that the intersection of two plane 778:, since all projective spaces of dimension 4898: 4884: 4876: 3666:, with 15 points, 35 lines and 15 planes. 3116:are distinct points and the lines through 1863:fundamental theorem of projective geometry 1705:. This means that, compared to elementary 1662:of the elements of the canonical basis of 333:It follows that the lines passing through 3632:1, 1, 1, 1, 0, 1, 1, 4, 0, ... (sequence 3336: 3320: 3304: 3292: 3058:(the set of points), together with a set 2867:was the study of common zeros of sets of 2779: 2771: 2688: 2678: 2672: 2650: 2640: 2633: 2632: 2615: 2605: 2599: 2577: 2561: 2540: 2535: 2529: 2498: 2473: 2448: 2429: 2406: 2384: 2378: 2377: 2362: 2345: 2328: 2315: 2310: 2305: 2303: 2250: 2240: 2229: 2208: 2206: 2165: 2149: 2130: 2111: 2105: 2005:{\displaystyle \pi :S\to \mathbf {P} (V)} 1988: 1974: 1246:. This projective subspace is called the 1043: 1029: 4795:An Introduction to Invariants and Moduli 4780:, esp. chapters I.2, I.7, II.5, and II.7 4278:; these are themselves special cases of 3522:-dimensional projective space over some 2737:, it results that projective spaces are 1721:") to Euclidean points, and vice versa. 1277:is a spanning set of a projective space 4423: 4342: 3294: 3207: 3030:Algebraic geometry of projective spaces 2792:{\displaystyle x\mapsto {\frac {1}{x}}} 2071:As soon as a basis has been chosen for 1462:vectors, any frame can be rewritten as 1297:, such an independent spanning set has 1075:to its equivalence class, which is the 831:has been chosen, and, in particular if 445:and the (projective) line at infinity. 4744:Euclidean and non-Euclidean geometries 4578:Linear Algebra and Projective Geometry 4465: 4453: 4159:, not just the locally free ones. See 3380:. Subspaces of dimension 0 are called 3052:can be defined axiomatically as a set 2183:{\displaystyle U_{i}=\{,x_{i}\neq 0\}} 1060:{\displaystyle p:V\to \mathbf {P} (V)} 456:may be identified with its associated 4541: 4166:, Chap. II, par. 4 for more details. 3652:The smallest projective plane is the 3143:Any line has at least 3 points on it. 2808:Real projective spaces have a simple 2277:has at least one nonzero coordinate. 1892:by the addition of new points called 1422:is a projective frame if and only if 1097:is a union of lines. It follows that 165:Projective spaces are widely used in 47:originated from the visual effect of 7: 4489: 3966:sheaves generated by global sections 3254:of the projective space is a subset 1779:Italian school of algebraic geometry 473:So, a projective space of dimension 51:, where parallel lines seem to meet 4654:, New York: John Wiley & Sons, 3537:Finite projective spaces and planes 3128:meet, then so do the lines through 2840:-cell with the quotient projection 1815:of the projective transformations). 806:The elements of a projective space 4478:Beutelspacher & Rosenbaum 1998 4386:Beutelspacher & Rosenbaum 1998 3470:(those that are isomorphic with a 3384:, those of dimension 1 are called 3272:(that is, completely contained in 1713:, for a given dimension, and that 105:, a projective space of dimension 14: 4783:Hilbert, D. and Cohn-Vossen, S.; 4432:Foundations of Translation Planes 1378:is the canonical projection from 261:, and the image is formed on the 4964: 4871:Projective Planes of Small Order 4456:, chapter 4.4. Projective bases. 3025:projective space as a manifold. 2209: 1989: 1825:This section is an excerpt from 1809:projective differential geometry 1685:This section is an excerpt from 1044: 300:to the intersection of the line 4820:Projective geometry. Vols. 1, 2 4669:Coxeter, Harold Scott MacDonald 4644:Coxeter, Harold Scott MacDonald 3876:with the underlying field  3394:then any subspace of dimension 3242:The three diagonal points of a 2974:morphism of algebraic varieties 1374:-dimensional vector space, and 1020:is a vector space over a field 565:under the equivalence relation 423:. By identifying each point of 239:, which may be considered as a 2881:fundamental theorem of algebra 2776: 2583: 2554: 2504: 2422: 2419: 2412: 2355: 2338: 2219: 2213: 2155: 2123: 1999: 1993: 1985: 1908:and allows using the tools of 1789:resulting in the study of the 1532:with a common nonzero factor. 1083:with the zero vector removed. 1054: 1048: 1040: 762:projective space of dimension 579:if there is a nonzero element 373:. This suggests to define the 308:does not belong to the plane ( 1: 4818:; Young, John Wesley (1965), 4717:, Band 44, Berlin, New York: 2946:are common zeros of a set of 2871:. These common zeros, called 2068:can be provided, as follows. 1016:be a projective space, where 915:Quaternionic projective space 477:can be defined as the set of 109:is defined as the set of the 96:axioms of projective geometry 4786:Geometry and the imagination 4522:Algebraic Theory of Lattices 4230:Generalizing to associative 4220:parametrize objects such as 3830:induce the same map between 3562:is a projective space where 2744:For example, in the case of 1969:, and consider the function 1281:, then there is a subset of 1162:are two different points of 4565:Encyclopedia of Mathematics 4309:Projective line over a ring 4236:projective line over a ring 3765:is not injective, it has a 2086:may be identified with its 1307:Contrarily to the cases of 1071:that maps a nonzero vector 663:is finite dimensional, the 491:This set can be the set of 452:with a distinguished point 200:, and more specifically in 5211: 4799:Cambridge University Press 4619:Cambridge University Press 4276:weighted projective spaces 3696:between two vector spaces 3540: 3027: 2953:Any affine variety can be 2883:asserts that a univariate 1942: 1824: 1703:projective transformations 1684: 1322: 1258:is a spanning set for it. 790:vector space of dimension 397:is a line passing through 127:. Equivalently, it is the 5166: 4962: 4831:(Reprint of 1910 edition) 4789:, 2nd ed. Chelsea (1999). 4746:, 2nd ed. Freeman (1980). 4558:Afanas'ev, V.V. (2001) , 4331:projective representation 4326:projective transformation 3748:is a non-zero element of 3708:over the same field  3491:Veblen & Young (1965) 3074:Each two distinct points 1965:in a normed vector space 1820:Projective transformation 1752:can be said to meet in a 1715:geometric transformations 685:In the common case where 511:(in a space of dimension 507:in a sphere of dimension 355:, and those contained in 59:, or, more generally, an 4650:Introduction to Geometry 4576:Baer, Reinhold (2005) , 4376:also referred to as the 4246:projective space bundles 4054:projective linear groups 3086:are in exactly one line. 2933:complex projective plane 2869:multivariate polynomials 1946:A projective space is a 1928:Pappus's hexagon theorem 1769:, the coordinates used ( 1767:complex projective space 1642:of the projective space 1446:and the coefficients of 1267:projectively independent 875:complex projective space 635:. This is the case when 603:topological vector space 206:non-orientable manifolds 4793:Mukai, Shigeru (2003), 4594:Berger, Marcel (2009), 4253:Severi–Brauer varieties 3964:). Using the notion of 3560:finite projective space 3484:non-Desarguesian planes 3414:subdirectly irreducible 3201:non-Desarguesian planes 2948:homogeneous polynomials 2944:homogeneous coordinates 2088:homogeneous coordinates 1813:differential invariants 1771:homogeneous coordinates 1611:are the coordinates of 1541:homogeneous coordinates 695:, the projective space 503:as the set of pairs of 245:three dimensional space 4705:Dembowski, P. (1968), 4380:and mistakenly as the 4069:Möbius transformations 3974:. The latter form the 3613:is usually written as 3555: 3355: 3000:Alexander Grothendieck 2907:of respective degrees 2885:square-free polynomial 2855:as the attaching map. 2793: 2722: 2708: 2518: 2260: 2245: 2184: 2006: 1950:, as endowed with the 1906:projective coordinates 1734:affine transformations 1658:consists of images by 1537:projective coordinates 1061: 930:is sometimes used for 843:projective coordinates 224: 36: 4502:Bachmann, F. (1959), 4304:Grassmannian manifold 4216:Even more generally, 4197:sequence of subspaces 4186:Grassmannian manifold 4147:quasi-coherent sheaf 4075:Dual projective space 3550: 3504:is isomorphic with a 3356: 2823:can be obtained from 2794: 2725:These charts form an 2720: 2709: 2519: 2266:since every point of 2261: 2225: 2190:is an open subset of 2185: 2056:to a neighborhood of 2052:, the restriction of 2012:that maps a point of 2007: 1857:to lines, and thus a 1726:transformation matrix 1348:points such that any 1062: 871:real projective space 786:to it (because every 605:, the quotient space 294:Cartesian coordinates 220:Projective plane and 219: 25:graphical perspective 22: 5082:Dimensions by number 4757:, Berlin, New York: 3574:Wedderburn's theorem 3495:Veblen–Young theorem 3291: 3246:are never collinear. 3197:theorem of Desargues 3193:Veblen–Young theorem 3167:consisting of a set 2961:, which consists of 2921:genus–degree formula 2915:consists of exactly 2804:CW complex structure 2770: 2528: 2302: 2205: 2104: 2035:, it follows that: 1973: 1805:projective varieties 1740:, the concept of an 1183:linearly independent 1028: 912:; see, for example, 817:are commonly called 678:is the dimension of 259:center of projection 254:Pinhole camera model 140:equivalence relation 5195:Space (mathematics) 5190:Projective geometry 4673:Projective geometry 4598:, Springer-Verlag, 4320:Projective geometry 4314:Space (mathematics) 4257:algebraic varieties 4112:-dimensional, then 3797:Birational geometry 3647:Bruck–Ryser theorem 3480:Desargues's theorem 3468:Desarguesian planes 3450:is equivalent to a 3418:compactly generated 3244:complete quadrangle 3150:incidence structure 2980:(that is, it is an 2873:algebraic varieties 2548: 1932:Desargues's theorem 1835:projective geometry 1746:perspective drawing 1699:projective geometry 1687:Projective geometry 1680:Projective geometry 1185:. It follows that: 1124:projective subspace 877:, respectively. If 620:, endowed with the 556:equivalence classes 493:equivalence classes 321:and is parallel to 175:projective geometry 43:, the concept of a 5011:Degrees of freedom 4914:Dimensional spaces 4847:"Projective Space" 4844:Weisstein, Eric W. 4755:Algebraic Geometry 4560:"projective space" 4518:Robert P. Dilworth 4516:Peter Crawley and 4378:Veblen–Young axiom 4259:over a field  4213:other subvarieties 4184:is generalized to 3784:is problematic if 3556: 3351: 3181:incidence relation 3041:synthetic geometry 3035:Synthetic geometry 2959:points at infinity 2940:projective variety 2865:algebraic geometry 2859:Algebraic geometry 2789: 2739:analytic manifolds 2735:analytic functions 2723: 2704: 2531: 2514: 2512: 2256: 2180: 2002: 1918:synthetic geometry 1914:incidence geometry 1894:points at infinity 1878:Euclidean geometry 1795:synthetic geometry 1787:Erlangen programme 1738:Euclidean geometry 1719:points at infinity 1707:Euclidean geometry 1220:synthetic geometry 1057: 241:central projection 225: 222:central projection 84:synthetic geometry 65:points at infinity 37: 5177: 5176: 4986:Lebesgue covering 4951:Algebraic variety 4808:978-0-521-80906-1 4768:978-0-387-90244-9 4751:Hartshorne, Robin 4742:Greenberg, M.J.; 4709:Finite geometries 4628:978-0-521-48277-6 4605:978-3-540-11658-5 4587:978-0-486-44565-6 4530:978-0-13-022269-5 4524:. Prentice-Hall. 4292:Geometric algebra 3199:and are known as 3179:of lines, and an 3173:of points, a set 3022:Proj construction 2897:zeros at infinity 2787: 2694: 2660: 2656: 2621: 2393: 2031:. As spheres are 1952:quotient topology 1948:topological space 1754:point at infinity 974:is often denoted 797:is isomorphic to 626:subspace topology 622:quotient topology 618:topological space 379:projective points 5202: 4974:Other dimensions 4968: 4936:Projective space 4900: 4893: 4886: 4877: 4861:Projective Space 4857: 4856: 4830: 4811: 4779: 4739: 4712: 4701: 4664: 4653: 4639: 4608: 4590: 4572: 4545: 4539: 4533: 4514: 4508: 4507: 4499: 4493: 4487: 4481: 4475: 4469: 4463: 4457: 4451: 4445: 4428: 4411: 4404: 4398: 4395: 4389: 4374: 4368: 4365: 4359: 4356: 4350: 4347: 4270: 4264: 4224:of a given kind. 4209: 4193: 4183: 4158: 4152: 4139: 4133: 4122: 4111: 4105: 4099: 4093: 4087: 4066: 4051: 4047: 4035: 4020: 3985: 3973: 3963: 3957: 3932: 3913: 3902: 3887: 3881: 3871: 3864: 3851: 3840: 3829: 3814: 3808: 3803:Two linear maps 3789: 3783: 3772: 3764: 3753: 3747: 3738: 3732: 3713: 3707: 3701: 3695: 3664: 3659: 3637: 3624: 3612: 3600: 3593: 3587: 3567: 3531: 3521: 3515: 3503: 3477: 3465: 3452:projective plane 3449: 3426:modular lattices 3400: 3393: 3379: 3373: 3360: 3358: 3357: 3352: 3341: 3340: 3325: 3324: 3312: 3311: 3286: 3277: 3271: 3265: 3259: 3220:Pappus's theorem 3187: 3178: 3172: 3166: 3139: 3133: 3127: 3121: 3115: 3109: 3103: 3097: 3085: 3079: 3069: 3063: 3057: 3051: 3045:projective space 3019: 2998:, introduced by 2978:Zariski topology 2918: 2914: 2910: 2905:algebraic curves 2901:Bézout's theorem 2894: 2890: 2854: 2839: 2834:by attaching an 2833: 2822: 2798: 2796: 2795: 2790: 2788: 2780: 2761: 2750: 2713: 2711: 2710: 2705: 2700: 2696: 2695: 2693: 2692: 2683: 2682: 2673: 2662: 2661: 2655: 2654: 2645: 2644: 2635: 2634: 2622: 2620: 2619: 2610: 2609: 2600: 2590: 2586: 2582: 2581: 2566: 2565: 2547: 2539: 2523: 2521: 2520: 2515: 2513: 2503: 2502: 2484: 2483: 2459: 2458: 2434: 2433: 2411: 2410: 2395: 2394: 2389: 2388: 2379: 2367: 2366: 2350: 2349: 2333: 2332: 2320: 2319: 2314: 2291:is associated a 2290: 2276: 2265: 2263: 2262: 2257: 2255: 2254: 2244: 2239: 2212: 2200: 2189: 2187: 2186: 2181: 2170: 2169: 2154: 2153: 2135: 2134: 2116: 2115: 2099: 2085: 2074: 2059: 2055: 2051: 2047: 2044:For every point 2029:antipodal points 2026: 2015: 2011: 2009: 2008: 2003: 1992: 1968: 1960: 1791:classical groups 1775:invariant theory 1759:Projective plane 1675: 1667: 1661: 1657: 1634: 1614: 1610: 1582: 1553: 1531: 1519: 1488: 1461: 1457: 1445: 1441: 1421: 1392: 1381: 1377: 1373: 1365: 1354: 1347: 1340: 1335:projective basis 1331:projective frame 1325:Projective frame 1303: 1296: 1292: 1288: 1284: 1280: 1276: 1272: 1264: 1257: 1253: 1245: 1241: 1237: 1213: 1199: 1180: 1176: 1172: 1161: 1150: 1136: 1118: 1107: 1096: 1092: 1082: 1074: 1066: 1064: 1063: 1058: 1047: 1023: 1019: 1015: 996:Related concepts 985: 973: 957: 949: 945: 929: 907: 895:projective plane 888: 882: 868: 861: 857: 840: 830: 816: 802: 796: 789: 781: 775: 769: 765: 758:is often called 757: 741: 730: 721: 705: 694: 681: 677: 662: 654: 644: 638: 634: 615: 600: 596: 586: 582: 578: 568: 564: 553: 542:projective space 539: 532: 517: 510: 505:antipodal points 502: 487: 476: 468:projectivization 455: 444: 431: 422: 412:line at infinity 409: 400: 396: 392: 384: 372: 363: 354: 345: 336: 329: 320: 316: 307: 303: 299: 291: 284: 280: 271: 263:projection plane 160:projective plane 152:antipodal points 149: 137: 126: 119: 108: 45:projective space 5210: 5209: 5205: 5204: 5203: 5201: 5200: 5199: 5180: 5179: 5178: 5173: 5162: 5141: 5077: 5015: 4969: 4960: 4926:Euclidean space 4909: 4904: 4842: 4841: 4838: 4814: 4809: 4792: 4769: 4759:Springer-Verlag 4749: 4729: 4719:Springer-Verlag 4704: 4683: 4667: 4662: 4642: 4629: 4612: 4606: 4593: 4588: 4575: 4557: 4554: 4549: 4548: 4540: 4536: 4515: 4511: 4501: 4500: 4496: 4488: 4484: 4476: 4472: 4464: 4460: 4452: 4448: 4434:, p. 506, 4429: 4425: 4420: 4415: 4414: 4405: 4401: 4396: 4392: 4375: 4371: 4366: 4362: 4357: 4353: 4348: 4344: 4339: 4298:Generalizations 4288: 4280:toric varieties 4266: 4260: 4222:elliptic curves 4205: 4200:More generally 4189: 4179: 4172: 4170:Generalizations 4165: 4154: 4148: 4135: 4128: 4113: 4107: 4101: 4100:. That is, if 4095: 4089: 4083: 4077: 4057: 4049: 4041: 4029: 4022: 3990: 3979: 3969: 3959: 3940: 3915: 3904: 3893: 3883: 3877: 3866: 3856: 3842: 3831: 3816: 3810: 3804: 3785: 3774: 3770: 3760: 3749: 3743: 3740: 3736: 3715: 3709: 3703: 3697: 3678: 3672: 3662: 3657: 3643: 3633: 3614: 3602: 3595: 3589: 3581: 3563: 3545: 3539: 3527: 3517: 3505: 3498: 3471: 3455: 3444: 3434: 3395: 3389: 3375: 3372: 3364: 3332: 3316: 3300: 3289: 3288: 3282: 3273: 3267: 3266:is a subset of 3261: 3255: 3183: 3174: 3168: 3152: 3135: 3129: 3123: 3117: 3111: 3105: 3099: 3093: 3081: 3075: 3065: 3059: 3053: 3047: 3037: 3032: 3015: 3010:, similarly as 2993: 2925:algebraic curve 2916: 2912: 2908: 2899:. For example, 2892: 2888: 2861: 2841: 2835: 2824: 2813: 2806: 2768: 2767: 2760: 2752: 2745: 2731:transition maps 2684: 2674: 2646: 2636: 2611: 2601: 2598: 2594: 2573: 2557: 2553: 2549: 2526: 2525: 2511: 2510: 2494: 2469: 2444: 2425: 2415: 2402: 2380: 2358: 2352: 2351: 2341: 2334: 2324: 2309: 2300: 2299: 2295:, which is the 2289: 2281: 2267: 2246: 2203: 2202: 2191: 2161: 2145: 2126: 2107: 2102: 2101: 2091: 2076: 2072: 2057: 2053: 2049: 2045: 2042: 2027:consist of two 2017: 2013: 1971: 1970: 1966: 1958: 1944: 1941: 1936: 1935: 1926:. Equivalently 1880:, and the term 1830: 1822: 1817: 1816: 1799:finite geometry 1711:Euclidean space 1690: 1682: 1673: 1663: 1659: 1651: 1643: 1640:canonical frame 1632: 1623: 1616: 1612: 1609: 1600: 1593: 1584: 1580: 1566: 1555: 1544: 1530: 1521: 1518: 1508: 1500: 1490: 1486: 1475: 1463: 1459: 1456: 1447: 1443: 1439: 1430: 1423: 1419: 1405: 1394: 1383: 1379: 1375: 1367: 1363: 1349: 1342: 1338: 1327: 1321: 1298: 1294: 1290: 1286: 1282: 1278: 1274: 1270: 1262: 1255: 1251: 1248:projective span 1243: 1239: 1235: 1228: 1204: 1190: 1178: 1174: 1163: 1152: 1141: 1127: 1109: 1098: 1094: 1090: 1088:linear subspace 1080: 1072: 1026: 1025: 1021: 1017: 1006: 1003: 998: 975: 967: 959: 955: 947: 939: 931: 919: 918:. The notation 905: 891:projective line 884: 878: 866: 859: 855: 832: 828: 807: 798: 791: 787: 779: 773: 772:the projective 767: 763: 751: 743: 732: 723: 715: 707: 696: 686: 679: 668: 660: 657:complex numbers 650: 640: 636: 629: 606: 598: 588: 584: 580: 570: 566: 559: 544: 537: 530: 524: 512: 508: 500: 482: 474: 453: 443: 437: 430: 424: 421: 415: 408: 402: 398: 394: 390: 387:projective line 382: 371: 365: 362: 356: 353: 347: 344: 338: 334: 328: 322: 318: 315: 309: 305: 301: 297: 286: 282: 279: 273: 269: 214: 202:manifold theory 171:affine geometry 156:projective line 147: 132: 121: 117: 106: 57:Euclidean space 29:vanishing point 17: 12: 11: 5: 5208: 5206: 5198: 5197: 5192: 5182: 5181: 5175: 5174: 5167: 5164: 5163: 5161: 5160: 5155: 5149: 5147: 5143: 5142: 5140: 5139: 5131: 5126: 5121: 5116: 5111: 5106: 5101: 5096: 5091: 5085: 5083: 5079: 5078: 5076: 5075: 5070: 5065: 5063:Cross-polytope 5060: 5055: 5050: 5048:Hyperrectangle 5045: 5040: 5035: 5029: 5027: 5017: 5016: 5014: 5013: 5008: 5003: 4998: 4993: 4988: 4983: 4977: 4975: 4971: 4970: 4963: 4961: 4959: 4958: 4953: 4948: 4943: 4938: 4933: 4928: 4923: 4917: 4915: 4911: 4910: 4905: 4903: 4902: 4895: 4888: 4880: 4874: 4873: 4868: 4858: 4837: 4836:External links 4834: 4833: 4832: 4816:Veblen, Oswald 4812: 4807: 4790: 4781: 4767: 4747: 4740: 4727: 4702: 4681: 4665: 4660: 4640: 4627: 4610: 4604: 4591: 4586: 4573: 4553: 4550: 4547: 4546: 4544:, example 3.72 4534: 4509: 4494: 4482: 4480:, pp. 6–7 4470: 4458: 4446: 4422: 4421: 4419: 4416: 4413: 4412: 4399: 4390: 4382:axiom of Pasch 4369: 4360: 4351: 4341: 4340: 4338: 4335: 4334: 4333: 4328: 4322: 4321: 4317: 4316: 4311: 4306: 4300: 4299: 4295: 4294: 4287: 4284: 4250: 4249: 4242: 4239: 4228: 4225: 4214: 4211: 4198: 4195: 4176: 4171: 4168: 4163: 4153:over a scheme 4076: 4073: 4048:.) The groups 4026:quotient group 3989: 3853:if and only if 3735: 3671: 3668: 3631: 3538: 3535: 3534: 3533: 3487: 3441: 3438: 3433: 3432:Classification 3430: 3368: 3350: 3347: 3344: 3339: 3335: 3331: 3328: 3323: 3319: 3315: 3310: 3307: 3303: 3299: 3296: 3248: 3247: 3232:characteristic 3228: 3227: 3216: 3215: 3145: 3144: 3141: 3087: 3064:of subsets of 3036: 3033: 3008:affine schemes 2992: 2989: 2976:is closed for 2860: 2857: 2812:structure, as 2805: 2802: 2786: 2783: 2778: 2775: 2756: 2729:, and, as the 2703: 2699: 2691: 2687: 2681: 2677: 2671: 2668: 2665: 2659: 2653: 2649: 2643: 2639: 2631: 2628: 2625: 2618: 2614: 2608: 2604: 2597: 2593: 2589: 2585: 2580: 2576: 2572: 2569: 2564: 2560: 2556: 2552: 2546: 2543: 2538: 2534: 2509: 2506: 2501: 2497: 2493: 2490: 2487: 2482: 2479: 2476: 2472: 2468: 2465: 2462: 2457: 2454: 2451: 2447: 2443: 2440: 2437: 2432: 2428: 2424: 2421: 2418: 2416: 2414: 2409: 2405: 2401: 2398: 2392: 2387: 2383: 2376: 2373: 2370: 2365: 2361: 2357: 2354: 2353: 2348: 2344: 2340: 2337: 2335: 2331: 2327: 2323: 2318: 2313: 2308: 2307: 2297:homeomorphisms 2285: 2253: 2249: 2243: 2238: 2235: 2232: 2228: 2224: 2221: 2218: 2215: 2211: 2179: 2176: 2173: 2168: 2164: 2160: 2157: 2152: 2148: 2144: 2141: 2138: 2133: 2129: 2125: 2122: 2119: 2114: 2110: 2037: 2033:compact spaces 2001: 1998: 1995: 1991: 1987: 1984: 1981: 1978: 1940: 1937: 1910:linear algebra 1831: 1823: 1821: 1818: 1811:(the study of 1750:parallel lines 1691: 1683: 1681: 1678: 1676:of their sum. 1668:(that is, the 1647: 1628: 1621: 1605: 1598: 1588: 1575: 1564: 1526: 1514: 1506: 1495: 1481: 1473: 1451: 1442:is a basis of 1435: 1428: 1414: 1403: 1323:Main article: 1320: 1317: 1227: 1224: 1216: 1215: 1201: 1173:, the vectors 1056: 1053: 1050: 1046: 1042: 1039: 1036: 1033: 1002: 999: 997: 994: 963: 935: 899:Riemann sphere 747: 711: 554:is the set of 523: 520: 441: 434:disjoint union 428: 419: 406: 369: 360: 351: 342: 326: 313: 277: 229:coplanar lines 213: 210: 185:; one for the 179:conic sections 103:linear algebra 73:parallel lines 15: 13: 10: 9: 6: 4: 3: 2: 5207: 5196: 5193: 5191: 5188: 5187: 5185: 5172: 5171: 5165: 5159: 5156: 5154: 5151: 5150: 5148: 5144: 5138: 5136: 5132: 5130: 5127: 5125: 5122: 5120: 5117: 5115: 5112: 5110: 5107: 5105: 5102: 5100: 5097: 5095: 5092: 5090: 5087: 5086: 5084: 5080: 5074: 5071: 5069: 5066: 5064: 5061: 5059: 5056: 5054: 5053:Demihypercube 5051: 5049: 5046: 5044: 5041: 5039: 5036: 5034: 5031: 5030: 5028: 5026: 5022: 5018: 5012: 5009: 5007: 5004: 5002: 4999: 4997: 4994: 4992: 4989: 4987: 4984: 4982: 4979: 4978: 4976: 4972: 4967: 4957: 4954: 4952: 4949: 4947: 4944: 4942: 4939: 4937: 4934: 4932: 4929: 4927: 4924: 4922: 4919: 4918: 4916: 4912: 4908: 4901: 4896: 4894: 4889: 4887: 4882: 4881: 4878: 4872: 4869: 4866: 4862: 4859: 4854: 4853: 4848: 4845: 4840: 4839: 4835: 4829: 4825: 4821: 4817: 4813: 4810: 4804: 4800: 4796: 4791: 4788: 4787: 4782: 4778: 4774: 4770: 4764: 4760: 4756: 4752: 4748: 4745: 4741: 4738: 4734: 4730: 4728:3-540-61786-8 4724: 4720: 4716: 4711: 4710: 4703: 4700: 4696: 4692: 4688: 4684: 4682:0-8020-2104-2 4678: 4674: 4670: 4666: 4663: 4661:0-471-18283-4 4657: 4652: 4651: 4645: 4641: 4638: 4634: 4630: 4624: 4620: 4616: 4611: 4607: 4601: 4597: 4592: 4589: 4583: 4579: 4574: 4571: 4567: 4566: 4561: 4556: 4555: 4551: 4543: 4538: 4535: 4531: 4527: 4523: 4519: 4513: 4510: 4505: 4498: 4495: 4491: 4486: 4483: 4479: 4474: 4471: 4467: 4462: 4459: 4455: 4450: 4447: 4444: 4443:0-8247-0609-9 4440: 4437: 4436:Marcel Dekker 4433: 4427: 4424: 4417: 4409: 4403: 4400: 4394: 4391: 4387: 4383: 4379: 4373: 4370: 4364: 4361: 4355: 4352: 4346: 4343: 4336: 4332: 4329: 4327: 4324: 4323: 4319: 4318: 4315: 4312: 4310: 4307: 4305: 4302: 4301: 4297: 4296: 4293: 4290: 4289: 4285: 4283: 4281: 4277: 4272: 4269: 4263: 4258: 4254: 4247: 4243: 4240: 4237: 4233: 4229: 4226: 4223: 4219: 4218:moduli spaces 4215: 4212: 4208: 4203: 4202:flag manifold 4199: 4196: 4192: 4187: 4182: 4177: 4174: 4173: 4169: 4167: 4162: 4157: 4151: 4146: 4141: 4138: 4131: 4126: 4120: 4116: 4110: 4104: 4098: 4092: 4086: 4082: 4074: 4072: 4070: 4064: 4060: 4055: 4045: 4039: 4033: 4027: 4018: 4014: 4010: 4006: 4002: 3998: 3994: 3988: 3986: 3983: 3977: 3972: 3967: 3962: 3955: 3951: 3947: 3943: 3939: 3938:automorphisms 3934: 3930: 3926: 3922: 3918: 3911: 3907: 3900: 3896: 3891: 3886: 3882:, the set of 3880: 3875: 3869: 3863: 3859: 3854: 3849: 3845: 3838: 3834: 3827: 3823: 3819: 3813: 3807: 3801: 3799: 3798: 3793: 3788: 3781: 3777: 3768: 3763: 3758: 3752: 3746: 3734: 3730: 3726: 3722: 3718: 3712: 3706: 3700: 3693: 3689: 3685: 3681: 3677: 3669: 3667: 3665: 3655: 3650: 3648: 3641: 3636: 3630: 3626: 3622: 3618: 3610: 3606: 3598: 3592: 3585: 3579: 3575: 3571: 3566: 3561: 3554: 3549: 3544: 3536: 3530: 3525: 3524:division ring 3520: 3513: 3509: 3501: 3496: 3492: 3488: 3485: 3481: 3475: 3469: 3463: 3459: 3453: 3447: 3442: 3439: 3436: 3435: 3431: 3429: 3427: 3423: 3419: 3415: 3411: 3406: 3404: 3398: 3392: 3387: 3383: 3378: 3371: 3367: 3361: 3348: 3345: 3342: 3337: 3333: 3329: 3326: 3321: 3317: 3313: 3308: 3305: 3301: 3297: 3285: 3279: 3276: 3270: 3264: 3258: 3253: 3245: 3241: 3240: 3239: 3237: 3233: 3225: 3224: 3223: 3222:as an axiom; 3221: 3213: 3212: 3211: 3209: 3208:Coxeter (1969 3204: 3202: 3198: 3194: 3189: 3186: 3182: 3177: 3171: 3164: 3160: 3156: 3151: 3142: 3138: 3132: 3126: 3120: 3114: 3108: 3102: 3096: 3092:'s axiom: If 3091: 3088: 3084: 3078: 3073: 3072: 3071: 3068: 3062: 3056: 3050: 3046: 3042: 3034: 3031: 3026: 3023: 3018: 3013: 3009: 3005: 3001: 2997: 2996:Scheme theory 2991:Scheme theory 2990: 2988: 2985: 2983: 2982:algebraic set 2979: 2975: 2970: 2968: 2964: 2960: 2956: 2951: 2949: 2945: 2941: 2936: 2934: 2930: 2929:singularities 2926: 2922: 2906: 2902: 2898: 2886: 2882: 2878: 2875:belong to an 2874: 2870: 2866: 2858: 2856: 2852: 2848: 2844: 2838: 2831: 2827: 2820: 2816: 2811: 2803: 2801: 2784: 2781: 2773: 2765: 2759: 2755: 2748: 2742: 2740: 2736: 2732: 2728: 2719: 2715: 2701: 2697: 2689: 2685: 2679: 2675: 2669: 2666: 2663: 2657: 2651: 2647: 2641: 2637: 2629: 2626: 2623: 2616: 2612: 2606: 2602: 2595: 2591: 2587: 2578: 2574: 2570: 2567: 2562: 2558: 2550: 2544: 2541: 2536: 2532: 2507: 2499: 2495: 2491: 2488: 2485: 2480: 2477: 2474: 2470: 2466: 2463: 2460: 2455: 2452: 2449: 2445: 2441: 2438: 2435: 2430: 2426: 2417: 2407: 2403: 2399: 2396: 2390: 2385: 2381: 2374: 2371: 2368: 2363: 2359: 2346: 2342: 2336: 2329: 2325: 2321: 2316: 2311: 2298: 2294: 2288: 2284: 2278: 2274: 2270: 2251: 2247: 2241: 2236: 2233: 2230: 2226: 2222: 2216: 2198: 2194: 2174: 2171: 2166: 2162: 2158: 2150: 2146: 2142: 2139: 2136: 2131: 2127: 2117: 2112: 2108: 2098: 2094: 2089: 2083: 2079: 2069: 2067: 2063: 2062:homeomorphism 2040: 2036: 2034: 2030: 2024: 2020: 1996: 1982: 1979: 1976: 1964: 1955: 1953: 1949: 1938: 1933: 1929: 1925: 1921: 1919: 1915: 1911: 1907: 1903: 1900:over a given 1899: 1895: 1891: 1890:affine spaces 1887: 1883: 1879: 1875: 1871: 1866: 1864: 1860: 1856: 1852: 1848: 1847:vector spaces 1844: 1840: 1836: 1828: 1819: 1814: 1810: 1806: 1802: 1800: 1796: 1792: 1788: 1784: 1780: 1776: 1772: 1768: 1763: 1761: 1760: 1755: 1751: 1747: 1743: 1739: 1735: 1731: 1727: 1722: 1720: 1716: 1712: 1708: 1704: 1700: 1696: 1688: 1679: 1677: 1671: 1666: 1655: 1650: 1646: 1641: 1636: 1631: 1627: 1620: 1615:on the basis 1608: 1604: 1597: 1591: 1587: 1578: 1574: 1570: 1563: 1559: 1551: 1547: 1542: 1538: 1533: 1529: 1524: 1517: 1512: 1504: 1498: 1493: 1484: 1479: 1471: 1467: 1454: 1450: 1438: 1434: 1427: 1417: 1413: 1409: 1402: 1398: 1390: 1386: 1371: 1360: 1358: 1352: 1345: 1336: 1332: 1326: 1318: 1316: 1314: 1313:affine spaces 1310: 1309:vector spaces 1305: 1301: 1268: 1265:of points is 1259: 1249: 1233: 1225: 1223: 1221: 1211: 1207: 1202: 1197: 1193: 1188: 1187: 1186: 1184: 1170: 1166: 1159: 1155: 1148: 1144: 1138: 1134: 1130: 1125: 1120: 1116: 1112: 1105: 1101: 1089: 1084: 1078: 1070: 1069:canonical map 1051: 1037: 1034: 1031: 1013: 1009: 1000: 995: 993: 991: 990: 983: 979: 971: 966: 962: 953: 943: 938: 934: 927: 923: 917: 916: 911: 910:division ring 902: 900: 896: 892: 887: 881: 876: 872: 863: 853: 848: 844: 839: 835: 826: 822: 821: 814: 810: 804: 801: 794: 785: 777: 761: 755: 750: 746: 739: 735: 729: 726: 719: 714: 710: 703: 699: 693: 689: 683: 675: 671: 666: 658: 653: 649:or the field 648: 643: 639:is the field 632: 627: 623: 619: 613: 609: 604: 595: 591: 577: 573: 562: 557: 551: 547: 543: 536: 529: 521: 519: 515: 506: 497: 494: 489: 485: 480: 471: 469: 465: 464: 459: 451: 446: 440: 435: 427: 418: 413: 405: 388: 380: 377:(called here 376: 368: 359: 350: 341: 331: 325: 312: 295: 289: 276: 266: 264: 260: 256: 255: 250: 246: 242: 238: 234: 230: 223: 218: 211: 209: 207: 203: 199: 194: 192: 188: 184: 180: 176: 172: 168: 163: 161: 157: 153: 145: 141: 135: 130: 124: 120:of dimension 116: 112: 104: 99: 97: 93: 89: 85: 81: 76: 74: 70: 66: 62: 58: 54: 50: 46: 42: 34: 30: 26: 21: 5168: 5134: 5073:Hyperpyramid 5038:Hypersurface 4935: 4931:Affine space 4921:Vector space 4850: 4819: 4794: 4784: 4754: 4743: 4708: 4672: 4649: 4614: 4595: 4577: 4563: 4537: 4521: 4512: 4503: 4497: 4492:, p. 71 4485: 4473: 4461: 4449: 4431: 4426: 4402: 4393: 4377: 4372: 4363: 4354: 4345: 4273: 4267: 4261: 4251: 4206: 4190: 4180: 4155: 4149: 4144: 4142: 4136: 4129: 4125:Grassmannian 4118: 4114: 4108: 4102: 4096: 4090: 4088:rather than 4084: 4078: 4062: 4058: 4043: 4031: 4023: 4016: 4012: 4008: 4004: 4000: 3996: 3992: 3981: 3970: 3960: 3953: 3949: 3945: 3941: 3935: 3928: 3924: 3920: 3916: 3909: 3905: 3898: 3894: 3884: 3878: 3874:identity map 3867: 3861: 3857: 3847: 3843: 3836: 3832: 3825: 3821: 3817: 3811: 3805: 3802: 3795: 3792:rational map 3786: 3779: 3775: 3769:larger than 3761: 3757:well-defined 3750: 3744: 3741: 3728: 3724: 3720: 3716: 3710: 3704: 3698: 3691: 3687: 3683: 3679: 3673: 3651: 3644: 3627: 3620: 3616: 3608: 3604: 3596: 3590: 3583: 3578:finite field 3569: 3564: 3559: 3557: 3528: 3518: 3511: 3507: 3499: 3473: 3461: 3457: 3445: 3422:complemented 3407: 3401:is called a 3396: 3390: 3385: 3381: 3376: 3369: 3365: 3362: 3283: 3280: 3274: 3268: 3262: 3256: 3251: 3249: 3236:Fano's axiom 3235: 3229: 3217: 3205: 3190: 3184: 3175: 3169: 3162: 3158: 3154: 3146: 3136: 3130: 3124: 3118: 3112: 3106: 3100: 3094: 3082: 3076: 3066: 3060: 3054: 3048: 3044: 3038: 3016: 2994: 2986: 2971: 2963:homogenizing 2954: 2952: 2937: 2932: 2896: 2891:has exactly 2877:affine space 2863:Originally, 2862: 2850: 2846: 2842: 2836: 2829: 2825: 2818: 2814: 2807: 2757: 2753: 2746: 2743: 2724: 2286: 2282: 2279: 2272: 2268: 2196: 2192: 2096: 2092: 2081: 2077: 2070: 2043: 2038: 2022: 2018: 1956: 1945: 1898:vector space 1881: 1867: 1859:collineation 1832: 1764: 1757: 1730:translations 1723: 1692: 1664: 1653: 1648: 1644: 1639: 1637: 1629: 1625: 1618: 1606: 1602: 1595: 1589: 1585: 1576: 1572: 1568: 1561: 1557: 1549: 1545: 1540: 1536: 1534: 1527: 1522: 1515: 1510: 1502: 1496: 1491: 1482: 1477: 1469: 1465: 1452: 1448: 1436: 1432: 1425: 1415: 1411: 1407: 1400: 1396: 1388: 1384: 1369: 1361: 1350: 1343: 1334: 1330: 1328: 1306: 1299: 1266: 1260: 1247: 1232:intersection 1229: 1217: 1209: 1205: 1203:A subset of 1195: 1191: 1168: 1164: 1157: 1153: 1146: 1142: 1139: 1132: 1128: 1123: 1121: 1114: 1110: 1103: 1099: 1085: 1068: 1011: 1007: 1004: 987: 981: 977: 969: 964: 960: 952:finite field 941: 936: 932: 925: 921: 913: 903: 889:is called a 885: 879: 864: 846: 837: 833: 818: 812: 808: 805: 799: 792: 771: 759: 753: 748: 744: 737: 733: 727: 724: 722:(as well as 717: 712: 708: 701: 697: 691: 687: 684: 673: 669: 664: 651: 647:real numbers 641: 630: 611: 607: 593: 589: 575: 571: 560: 549: 545: 541: 528:vector space 525: 513: 498: 490: 483: 479:vector lines 472: 461: 458:vector space 450:affine space 447: 438: 425: 416: 411: 403: 386: 378: 374: 366: 357: 348: 339: 332: 323: 310: 287: 274: 267: 262: 258: 252: 226: 195: 164: 133: 129:quotient set 122: 115:vector space 111:vector lines 100: 91: 87: 77: 61:affine space 52: 44: 38: 5158:Codimension 5137:-dimensions 5058:Hypersphere 4941:Free module 4468:, chapter 4 4466:Berger 2009 4454:Berger 2009 4227:other rings 4067:are called 4052:are called 3794:, see also 3676:linear maps 3493:proved the 3363:A subspace 2524:such that 1963:unit sphere 1916:, see also 1874:projections 1870:perspective 1843:isomorphism 1783:Felix Klein 1695:mathematics 1554:on a frame 1543:of a point 1285:that spans 1079:containing 1077:vector line 845:of a point 706:is denoted 682:minus one. 569:defined by 237:perspective 144:unit sphere 53:at infinity 49:perspective 41:mathematics 5184:Categories 5153:Hyperspace 5033:Hyperplane 4865:PlanetMath 4596:Geometry I 4552:References 4542:Mukai 2003 4408:Fano plane 4134:planes in 4081:dual space 3914:is simply 3767:null space 3674:Injective 3654:Fano plane 3553:Fano plane 3403:hyperplane 3028:See also: 2967:saturating 2887:of degree 2810:CW complex 2100:, the set 2095:= 0, ..., 1882:homography 1853:that maps 1839:homography 1827:Homography 1489:such that 1476:), ..., p( 1357:hyperplane 1304:elements. 958:elements, 784:isomorphic 587:such that 522:Definition 212:Motivation 183:hyperbolas 5043:Hypercube 5021:Polytopes 5001:Minkowski 4996:Hausdorff 4991:Inductive 4956:Spacetime 4907:Dimension 4852:MathWorld 4580:, Dover, 4570:EMS Press 4532:, p. 109. 4490:Baer 2005 4418:Citations 4175:dimension 3999:)) = Aut( 3890:morphisms 3865:for some 3670:Morphisms 3330:⋯ 3327:⊂ 3314:⊂ 3306:− 3295:∅ 3012:manifolds 2955:completed 2927:from its 2777:↦ 2764:real line 2667:… 2658:^ 2627:… 2571:⋯ 2542:− 2533:φ 2489:⋯ 2453:− 2439:⋯ 2420:↦ 2400:… 2391:^ 2372:… 2339:→ 2312:φ 2227:⋃ 2172:≠ 2140:⋯ 1986:→ 1977:π 1886:Euclidean 1851:bijection 1041:→ 665:dimension 80:isotropic 69:direction 5170:Category 5146:See also 4946:Manifold 4753:(1977), 4671:(1969), 4646:(1974), 4520:, 1973. 4286:See also 4241:patching 3888:-linear 3663:PG(3, 2) 3658:PG(2, 2) 3478:satisfy 3252:subspace 3234:include 2280:To each 1939:Topology 1601:+ ... + 1567:), ..., 1509:+ ... + 1406:), ..., 1001:Subspace 526:Given a 233:parallel 198:topology 191:ellipses 187:parabola 167:geometry 31:(on the 5068:Simplex 5006:Fractal 4828:0179666 4777:0463157 4737:0233275 4691:0346652 4637:1629468 4123:is the 4015:=: PGL( 3638:in the 3635:A001231 3410:lattice 3020:. The 3004:schemes 2931:in the 2201:, and 1961:be the 1624:, ..., 1431:, ..., 1393:, then 1067:be the 1024:, and 989:PG(3,2) 823:. If a 655:of the 645:of the 624:of the 533:over a 292:, when 247:onto a 243:of the 150:in two 138:by the 33:horizon 5025:shapes 4826:  4805:  4775:  4765:  4735:  4725:  4699:977732 4697:  4689:  4679:  4658:  4635:  4625:  4602:  4584:  4528:  4441:  4038:center 3759:. (If 3742:where 3526:  3516:, the 3472:PG(2, 3466:. The 3382:points 3090:Veblen 2090:. For 1841:is an 1807:) and 1781:, and 1777:, the 1670:tuples 1366:is an 1261:A set 1254:, and 1230:Every 1086:Every 841:, the 820:points 776:-space 540:, the 448:As an 375:points 101:Using 5129:Eight 5124:Seven 5104:Three 4981:Krull 4337:Notes 4232:rings 4145:every 4007:= GL( 3976:group 3892:from 3733:via: 3607:, GF( 3570:order 3386:lines 2938:So a 2727:atlas 2293:chart 2066:atlas 2060:is a 1924:field 1902:field 1855:lines 1742:angle 1732:(the 1583:with 1319:Frame 1273:. If 1200:, and 986:(see 954:with 950:is a 946:. If 908:is a 893:or a 873:or a 852:up to 825:basis 770:, or 766:over 659:. If 633:\ {0} 616:is a 601:is a 597:. If 563:\ {0} 535:field 460:(see 251:(see 249:plane 136:\ {0} 88:point 63:with 5114:Five 5109:Four 5089:Zero 5023:and 4803:ISBN 4763:ISBN 4723:ISBN 4695:OCLC 4677:ISBN 4656:ISBN 4623:ISBN 4600:ISBN 4582:ISBN 4526:ISBN 4439:ISBN 4255:are 4042:Aut( 4024:the 4011:) / 4003:) / 3991:Aut( 3948:) → 3936:The 3841:and 3809:and 3723:) → 3702:and 3640:OEIS 3551:The 3134:and 3122:and 3080:and 3043:, a 2911:and 2733:are 1957:Let 1930:and 1888:and 1872:and 1837:, a 1728:and 1638:The 1535:The 1372:+ 1) 1311:and 1226:Span 1181:are 1177:and 1151:and 1005:Let 782:are 385:. A 92:line 90:and 5119:Six 5099:Two 5094:One 4863:at 4161:EGA 4132:− 1 4127:of 4106:is 4050:PGL 4040:of 4030:GL( 4028:of 3980:GL( 3903:to 3870:≠ 0 3815:in 3800:.) 3771:{0} 3615:PG( 3603:PG( 3599:+ 1 3582:GF( 3506:PG( 3502:≥ 3 3456:PG( 3448:= 2 3399:− 1 3039:In 2749:= 1 2048:of 1876:in 1833:In 1785:'s 1693:In 1539:or 1382:to 1362:If 1353:+ 1 1346:+ 2 1333:or 1302:+ 1 1293:is 1250:of 1218:In 1140:If 1093:of 992:). 976:PG( 920:PG( 865:If 858:in 827:of 803:). 795:+ 1 760:the 731:or 667:of 628:of 583:of 558:of 518:). 516:+ 1 486:+ 1 436:of 414:of 290:= 1 196:In 146:of 131:of 125:+ 1 71:of 39:In 23:In 5186:: 4849:. 4824:MR 4801:, 4773:MR 4771:, 4761:, 4733:MR 4731:, 4721:, 4713:, 4693:, 4687:MR 4685:, 4633:MR 4631:, 4621:, 4617:, 4568:, 4562:, 4282:. 4271:. 4164:II 4140:. 4071:. 3933:. 3931:)) 3927:, 3862:λS 3860:= 3824:, 3737:→ 3690:, 3682:∈ 3656:, 3649:. 3625:. 3619:, 3611:)) 3580:, 3558:A 3510:, 3476:)) 3460:, 3428:. 3424:, 3420:, 3416:, 3405:. 3250:A 3238:; 3161:, 3157:, 3137:bd 3131:ac 3125:cd 3119:ab 3110:, 3104:, 3098:, 2950:. 2935:. 2917:de 2845:→ 2741:. 1801:. 1697:, 1594:= 1592:+1 1581:)) 1579:+1 1501:= 1499:+1 1487:)) 1485:+1 1455:+1 1420:)) 1418:+1 1359:. 1329:A 1137:. 1122:A 1119:. 980:, 924:, 901:. 836:= 690:= 594:λy 592:= 574:~ 330:. 302:OP 265:. 208:. 193:. 162:. 86:, 75:. 35:). 5135:n 4899:e 4892:t 4885:v 4867:. 4855:. 4384:( 4268:K 4262:K 4248:. 4238:. 4210:. 4207:V 4194:. 4191:V 4181:V 4156:Y 4150:E 4137:V 4130:n 4121:) 4119:V 4117:( 4115:P 4109:n 4103:V 4097:V 4091:V 4085:V 4065:) 4063:C 4061:( 4059:P 4046:) 4044:V 4034:) 4032:V 4021:, 4019:) 4017:V 4013:K 4009:V 4005:K 4001:V 3997:V 3995:( 3993:P 3984:) 3982:V 3971:V 3961:K 3956:) 3954:V 3952:( 3950:P 3946:V 3944:( 3942:P 3929:W 3925:V 3923:( 3921:L 3919:( 3917:P 3912:) 3910:W 3908:( 3906:P 3901:) 3899:V 3897:( 3895:P 3885:K 3879:K 3868:λ 3858:T 3850:) 3848:W 3846:( 3844:P 3839:) 3837:V 3835:( 3833:P 3828:) 3826:W 3822:V 3820:( 3818:L 3812:T 3806:S 3787:v 3782:) 3780:v 3778:( 3776:T 3762:T 3751:V 3745:v 3739:, 3731:) 3729:W 3727:( 3725:P 3721:V 3719:( 3717:P 3711:K 3705:W 3699:V 3694:) 3692:W 3688:V 3686:( 3684:L 3680:T 3642:) 3623:) 3621:q 3617:n 3609:q 3605:n 3597:q 3591:q 3586:) 3584:q 3565:P 3532:. 3529:K 3519:n 3514:) 3512:K 3508:n 3500:n 3486:. 3474:K 3464:) 3462:K 3458:d 3446:n 3397:n 3391:n 3377:i 3370:i 3366:X 3349:. 3346:P 3343:= 3338:n 3334:X 3322:0 3318:X 3309:1 3302:X 3298:= 3284:n 3275:X 3269:X 3263:X 3257:X 3185:I 3176:L 3170:P 3165:) 3163:I 3159:L 3155:P 3153:( 3140:. 3113:d 3107:c 3101:b 3095:a 3083:q 3077:p 3067:P 3061:L 3055:P 3049:S 3017:R 2913:e 2909:d 2893:n 2889:n 2853:) 2851:R 2849:( 2847:P 2843:S 2837:n 2832:) 2830:R 2828:( 2826:P 2821:) 2819:R 2817:( 2815:P 2785:x 2782:1 2774:x 2758:i 2754:U 2747:n 2702:, 2698:) 2690:i 2686:x 2680:n 2676:x 2670:, 2664:, 2652:i 2648:x 2642:i 2638:x 2630:, 2624:, 2617:i 2613:x 2607:0 2603:x 2596:( 2592:= 2588:) 2584:] 2579:n 2575:x 2568:: 2563:0 2559:x 2555:[ 2551:( 2545:1 2537:i 2508:, 2505:] 2500:n 2496:y 2492:: 2486:: 2481:1 2478:+ 2475:i 2471:y 2467:: 2464:1 2461:: 2456:1 2450:i 2446:y 2442:: 2436:: 2431:0 2427:y 2423:[ 2413:) 2408:n 2404:y 2397:, 2386:i 2382:y 2375:, 2369:, 2364:0 2360:y 2356:( 2347:i 2343:U 2330:n 2326:R 2322:: 2317:i 2287:i 2283:U 2275:) 2273:V 2271:( 2269:P 2252:i 2248:U 2242:n 2237:0 2234:= 2231:i 2223:= 2220:) 2217:V 2214:( 2210:P 2199:) 2197:V 2195:( 2193:P 2178:} 2175:0 2167:i 2163:x 2159:, 2156:] 2151:n 2147:x 2143:: 2137:: 2132:0 2128:x 2124:[ 2121:{ 2118:= 2113:i 2109:U 2097:n 2093:i 2084:) 2082:V 2080:( 2078:P 2073:V 2058:P 2054:π 2050:S 2046:P 2041:. 2025:) 2023:V 2021:( 2019:P 2014:S 2000:) 1997:V 1994:( 1990:P 1983:S 1980:: 1967:V 1959:S 1829:. 1689:. 1674:p 1665:K 1660:p 1656:) 1654:K 1652:( 1649:n 1645:P 1633:) 1630:n 1626:e 1622:0 1619:e 1617:( 1613:v 1607:n 1603:e 1599:0 1596:e 1590:n 1586:e 1577:n 1573:e 1571:( 1569:p 1565:0 1562:e 1560:( 1558:p 1556:( 1552:) 1550:v 1548:( 1546:p 1528:i 1525:′ 1523:e 1516:n 1513:′ 1511:e 1507:0 1505:′ 1503:e 1497:n 1494:′ 1492:e 1483:n 1480:′ 1478:e 1474:0 1472:′ 1470:e 1468:( 1466:p 1464:( 1460:n 1453:n 1449:e 1444:V 1440:) 1437:n 1433:e 1429:0 1426:e 1424:( 1416:n 1412:e 1410:( 1408:p 1404:0 1401:e 1399:( 1397:p 1395:( 1391:) 1389:V 1387:( 1385:P 1380:V 1376:p 1370:n 1368:( 1364:V 1351:n 1344:n 1339:n 1300:n 1295:n 1291:P 1287:P 1283:S 1279:P 1275:S 1271:S 1263:S 1256:S 1252:S 1244:S 1240:S 1236:S 1212:) 1210:V 1208:( 1206:P 1198:) 1196:V 1194:( 1192:P 1179:w 1175:v 1171:) 1169:V 1167:( 1165:P 1160:) 1158:w 1156:( 1154:p 1149:) 1147:v 1145:( 1143:p 1135:) 1133:V 1131:( 1129:P 1117:) 1115:W 1113:( 1111:P 1106:) 1104:W 1102:( 1100:p 1095:V 1091:W 1081:v 1073:v 1055:) 1052:V 1049:( 1045:P 1038:V 1035:: 1032:p 1022:K 1018:V 1014:) 1012:V 1010:( 1008:P 984:) 982:q 978:n 972:) 970:K 968:( 965:n 961:P 956:q 948:K 944:) 942:K 940:( 937:n 933:P 928:) 926:K 922:n 906:K 886:n 880:n 867:K 860:K 856:λ 847:P 838:K 834:V 829:V 815:) 813:V 811:( 809:P 800:K 793:n 788:K 780:n 774:n 768:K 764:n 756:) 754:K 752:( 749:n 745:P 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Index


graphical perspective
vanishing point
horizon
mathematics
perspective
Euclidean space
affine space
points at infinity
direction
parallel lines
isotropic
synthetic geometry
axioms of projective geometry
linear algebra
vector lines
vector space
quotient set
equivalence relation
unit sphere
antipodal points
projective line
projective plane
geometry
affine geometry
projective geometry
conic sections
hyperbolas
parabola
ellipses

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