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Talk:First uncountable ordinal

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84: 74: 53: 22: 288:
Nevermind, I was mistaken. "Countably compact" means every countable cover has a finite subcover. "Lindelof" means every cover has a countable subcover. "Compact" means every cover has a finite subcover. It is obvious that a countably compact space is compact if and only if Lindelof.
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I added Jech's book as a reference. This is perhaps overkill, any book on Set Theory will define omega_1. (Kunen, Komjath, Just+Weese, Drake+Singh, Deiser, ...) Also some books in Algebra and/or Analysis will define omega_1 and at least mention some basic properties.
140: 273:"a countably compact space is compact if and only if it is Lindelöf" I believe that this is only true for T1 spaces, though I don't have a counterexample in mind. 318: 130: 313: 106: 97: 58: 33: 21: 176: 195: 278: 39: 83: 164: 290: 274: 232: 105:
on Knowledge. If you would like to participate, please visit the project page, where you can join
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is not ω. Any continuous function from to the reals must be constant on for some α<ω
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I also added "Counterexamples in topology" for the topological properties.
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and in my topology reference. I'll go ahead and change it.
101:, a collaborative effort to improve the coverage of 182:I think it is countably compact, and so it says in 8: 19: 47: 49: 7: 95:This article is within the scope of 38:It is of interest to the following 14: 319:Mid-priority mathematics articles 115:Knowledge:WikiProject Mathematics 314:Start-Class mathematics articles 118:Template:WikiProject Mathematics 82: 72: 51: 20: 269:Compact if and only if Lindelof 135:This article has been rated as 1: 109:and see a list of open tasks. 159:"The topological space [0,ω 335: 299:22:33, 5 April 2023 (UTC) 283:00:27, 5 April 2023 (UTC) 134: 67: 46: 264:15:52, 23 May 2011 (UTC) 237:19:09, 6 June 2011 (UTC) 141:project's priority scale 98:WikiProject Mathematics 28:This article is rated 165:sequentially compact 121:mathematics articles 90:Mathematics portal 34:content assessment 177:countably compact 155: 154: 151: 150: 147: 146: 326: 197: 196: 158: 123: 122: 119: 116: 113: 92: 87: 86: 76: 69: 68: 63: 55: 48: 31: 25: 24: 16: 334: 333: 329: 328: 327: 325: 324: 323: 304: 303: 271: 245: 226: 219:, that is, its 217:regular ordinal 214: 209:axiom of choice 162: 120: 117: 114: 111: 110: 88: 81: 61: 32:on Knowledge's 29: 12: 11: 5: 332: 330: 322: 321: 316: 306: 305: 302: 301: 270: 267: 244: 241: 240: 239: 224: 212: 184:Order topology 160: 157: 156: 153: 152: 149: 148: 145: 144: 133: 127: 126: 124: 107:the discussion 94: 93: 77: 65: 64: 56: 44: 43: 37: 26: 13: 10: 9: 6: 4: 3: 2: 331: 320: 317: 315: 312: 311: 309: 300: 296: 292: 287: 286: 285: 284: 280: 276: 268: 266: 265: 261: 257: 252: 249: 242: 238: 234: 230: 222: 218: 211:holds, then ω 210: 206: 205: 204: 202: 200: 198: 193: 189: 185: 180: 178: 174: 170: 166: 142: 138: 132: 129: 128: 125: 108: 104: 100: 99: 91: 85: 80: 78: 75: 71: 70: 66: 60: 57: 54: 50: 45: 41: 35: 27: 23: 18: 17: 272: 253: 250: 246: 203: 201: 199: 181: 137:Mid-priority 136: 96: 62:Mid‑priority 40:WikiProjects 112:Mathematics 103:mathematics 59:Mathematics 30:Start-class 308:Categories 243:References 221:cofinality 171:(nor even 229:JRSpriggs 291:DanRaies 275:DanRaies 173:Lindelöf 167:but not 207:If the 188:YohanN7 169:compact 139:on the 256:Aleph4 36:scale. 215:is a 179:). " 163:) is 295:talk 279:talk 260:talk 233:talk 192:talk 175:or 131:Mid 310:: 297:) 281:) 262:) 254:-- 235:) 227:. 194:) 293:( 277:( 258:( 231:( 225:1 213:1 190:( 161:1 143:. 42::

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Mathematics portal
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mathematics
the discussion
Mid
project's priority scale
sequentially compact
compact
Lindelöf
countably compact
Order topology
YohanN7
talk
axiom of choice
regular ordinal
cofinality
JRSpriggs
talk
19:09, 6 June 2011 (UTC)
Aleph4
talk
15:52, 23 May 2011 (UTC)
DanRaies

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