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References to 'union'
1. $F_\sigma$ set by rspuzio
2. $m$-system by CWoo
3. $\mathbb{R}^n$ is not a countable union of proper vector subspaces by rspuzio
4. $\sigma$-algebra by drini
5. $\sigma$-finite by Koro
6. a compact metric space is second countable by azdbacks4234
7. a compact set in a Hausdorff space is closed by mathcam
8. a space is compact iff any family of closed sets having fip has non-empty intersection by CWoo
9. a space is T1 if and only if every singleton is closed by waj
10. a space is T1 if and only if every subset A is the intersection of all open sets containing A by waj
11. abstract family of languages by CWoo
12. additive by Andrea Ambrosio
13. algebraic lattice by CWoo
14. alternative characterization of ultrafilter by yark
15. alternative characterizations of Noetherian topological spaces, proof of by yark
16. ambiguous grammar by CWoo
17. analytic set by gel
18. antiderivative by asteroid
19. area bounded by arc and two lines by pahio
20. area of a polygonal region by Mathprof
21. atom by CWoo
22. automatic presentation by mathcam
23. axiom of choice by GrafZahl
24. axiom of countable choice by yark
25. axiom of dependent choices by CWoo
26. Baire category theorem by Koro
27. Banach-Tarski paradox by paolini
28. basis (topology) by rspuzio
29. Bayes' theorem by akrowne
30. beyond formalism: G\"{o}del's incompleteness by gribskoff
31. blocks of permutation groups by rm50
32. Boolean operations on automata by CWoo
33. Boolean subalgebra by CWoo
34. Bourbaki, Nicolas by Daume
35. Brauer's ovals theorem by Andrea Ambrosio
36. Brouwerian lattice by CWoo
37. canonical ordering on pairs of ordinals by CWoo
38. cardinal arithmetic by yark
39. Cartan's umbrella by jirka
40. Cartesian product by djao
41. characteristic function by bbukh
42. clopen subset by mathcam
43. closed set by yark
44. closure properties on languages by CWoo
45. cofinality by yark
46. compactness is preserved under a continuous map by yark
47. comparison between Lebesgue and Riemann Integration by Mathprof
48. complexity class by Henry
49. concepts in set theory by matte
50. congruence relation on an algebraic system by CWoo
51. connected graph by rspuzio
52. context-free language by CWoo
53. context-sensitive language by CWoo
54. continuous relation by CWoo
55. convex set by drini
56. current by paolini
57. de Morgan's laws by mathcam
58. Dedekind cuts by rmilson
59. definite language by CWoo
60. definition of prime ideal by Artin by pahio
61. derivation of properties of regular open set by CWoo
62. derived Boolean operations by CWoo
63. descriptive metadata specification by yi6604
64. deterministic pushdown automaton by CWoo
65. Dilworth's theorem by CWoo
66. disjoint union by yark
67. double coset by yark
68. Efim Zelmanov by PrimeFan
69. enumerative combinatorics by mps
70. equivalence of Hausdorff's maximum principle, Zorn's lemma and the well-ordering theorem by mathcam
71. equivalence of Zorn's lemma and the axiom of choice by Henry
72. equivalent defining conditions on a Noetherian ring by CWoo
73. every $\sigma$-compact set is Lindel\"of by joen235
74. every bounded sequence has limit along an ultrafilter by kompik
75. every Hilbert space has an orthonormal basis by asteroid
76. example of a probabilistic proof by bbukh
77. example of a universal structure by uzeromay
78. example of Aronszajn tree by Henry
79. example of Boolean algebras by CWoo
80. example of universe of finite sets by rspuzio
81. examples of countable sets by CWoo
82. examples of ring of sets by rspuzio
83. extending a capacity to a Cartesian product by gel
84. exterior algebra by rmilson
85. Fields medal by Mravinci
86. finite fields of sets by rspuzio
87. free semigroup with involution by Mazzu
88. from Hilbert's tenth problem to G\"{o}del's trichotomy by gribskoff
89. fuzzy subset by ggerla
90. Galois representation by alozano
91. generalized Boolean algebra by CWoo
92. Giuseppe Peano by PrimeFan
93. Hausdorff's maximum principle by CWoo
94. hitting times are stopping times by gel
95. Horn clause by PrimeFan
96. improper integral by paolini
97. index of set theory by rspuzio
98. indexing set by Wkbj79
99. induction by Daume
100. insertion operation on languages by CWoo
101. interpretation of well-formed formulas by CWoo
102. irreducible by mathcam
103. kernel of a homomorphism between algebraic systems by CWoo
104. Kleene's theorem by CWoo
105. Kuratowski closure-complement theorem by CWoo
106. language by mps
107. lattice homomorphism by CWoo
108. lattice of fields by CWoo
109. Levy collapse by ratboy
110. Lindenmayer system by CWoo
111. long line by Dr_Absentius
112. manifold by matte
113. matroid by mps
114. measure by djao
115. multiplicatively closed by CWoo
116. multiset by PrimeFan
117. Myhill-Nerode theorem for semigroups by Ziosilvio
118. Nerode equivalence by Ziosilvio
119. neutrosophic logic by para0doxa
120. neutrosophic probability by para0doxa
121. neutrosophic set by para0doxa
122. no continuous function switches the rational and the irrational numbers by yark
123. no countable dense subset of a complete metric space is a $G_\delta$ by gumau
124. non-standard analysis by PrimeFan
125. normal subgroups of the symmetric groups by rm50
126. o-minimality by Timmy
127. open set by mathwizard
128. ordered geometry by CWoo
129. ordinal space by CWoo
130. Ostrowski theorem by Andrea Ambrosio
131. paradox of the binary tree by WM
132. Parikh's theorem by CWoo
133. pentagonal number theorem by bbukh
134. point preventing uniform convergence by pahio
135. polynomial ring by djao
136. predicativism by gribskoff
137. product of non-empty set of non-empty sets is non-empty by CWoo
138. product topology by CWoo
139. projections of analytic sets are analytic by gel
140. projective variety by mathcam
141. proof of alternative characterization of ultrafilter by rspuzio
142. proof of Banach-Tarski paradox by GrafZahl
143. proof of basic theorem about ordered groups by rspuzio
144. proof of Brouwer fixed point theorem by uriw
145. proof of Choquet's capacitability theorem by gel
146. proof of class equation theorem by gumau
147. proof of compact pavings are closed subsets of a compact space by gel
148. proof of exhaustion by compact sets for $\mathbb{R}^n$ by cvalente
149. proof of extending a capacity to a Cartesian product by gel
150. proof of Ramsey's theorem by mathcam
151. proof of Riemann mapping theorem by rspuzio
152. proof of the uniformization theorem by Simone
153. proof of Tukey's lemma by Koro
154. proof of Vitali convergence theorem by stevecheng
155. proof that a finite collection of sets will not suffice by rspuzio
156. proof that a relation is union of functions if and only if AC by ratboy
157. proof that products of connected spaces are connected by yark
158. proof that the rationals are countable by alozano
159. properties of functions by yark
160. properties of linear independence by CWoo
161. properties of non-archimedean valuations by rm50
162. pseudoparadox in measure theory by rspuzio
163. quotient group of a topological group by its identity component is totally disconnected by joking
164. rational set by CWoo
165. real closed fields by mathcam
166. regular expression by CWoo
167. regular language by mps
168. regular open set by CWoo
169. relation algebra by CWoo
170. relation as union of functions by Mathprof
171. ring of sets by CWoo
172. saturated by drini
173. saturated (set) by drini
174. scattered space by CWoo
175. semicontinuous by bwebste
176. set by Mathprof
177. set theory by mathwizard
178. sheaf of sections by guffin
179. sign relation by Jon Awbrey
180. simplicial complex by djao
181. small integers that are or might be the largest of their kind by Mravinci
182. Smarandache geometries by jonnathan
183. star-free by CWoo
184. subanalytic set by jirka
185. support of integrable function with respect to counting measure is countable by Wkbj79
186. syntactic congruence by Ziosilvio
187. tangent plane (elementary) by rspuzio
188. Tarski-Seidenberg theorem by jirka
189. the set of all real transcendental numbers is uncountable by gilbert_51126
190. topology via converging nets by CWoo
191. triadic relation by Jon Awbrey
192. uniform convergence on union interval by pahio
193. union of countable sets by CWoo
194. Van Kampen's theorem by RonaldBrown
195. Van Kampen's theorem result by mathcam
196. volume of solid of revolution by pahio
197. Zermelo-Fraenkel axioms by mathcam
198. zero set of a topological space by CWoo
199. Zorn's lemma and bases for vector spaces by CWoo