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and initiated the study of infinite numbers, now a major branch of [[set theory]].

{{r|Set theory}}

| title = Classical descriptive set theory

{{r|Complement (set theory)}}

{{rpl|Fibre (set theory)}}

...rel; see [[Non-Borel_set/Advanced]] if you are acquainted with descriptive set theory. If you are not, you may find it instructive to try proving that ''A'' is B

...ins ''X'' itself and is closed under the operation of taking [[complement (set theory)|complement]]s, finite [[union]]s and finite [[intersection]]s in ''X''. Th

In [[set theory]], the '''kernel of a function''' is the [[equivalence relation]] on the do

{{r|Set theory}}

*In [[mathematics]], the term ''element'' is mainly used in [[set theory]], and in various combinations:

In [[set theory]], the '''symmetric difference''' of two sets is the set of elements that b

{{r|Set theory}}

...hen considered as a partially [[ordered set]] with respect to [[inclusion (set theory)|inclusion]].

{{r|Set theory}}

* {{cite book | author=Paul Halmos | authorlink=Paul Halmos | title=Naive set theory | series=The University Series in Undergraduate Mathematics | publisher=[[V ...h J. Devlin | authorlink=Keith Devlin | title=Fundamentals of Contemporary Set Theory | series=Universitext | publisher=[[Springer-Verlag]] | year=1979 | isbn=0-

{{r|Class (set theory)|In mathematics}}

...closed if <math>X-A=\{x \in X \mid x \notin A\}</math>, the [[complement (set theory)|complement]] of <math>A</math> in <math>X</math>, is an [[open set]]. The

In [[set theory]], a '''transitive relation''' on a [[set (mathematics)|set]] is a [[relati

* In [[set theory]], [[intersection]] and [[union]];

* {{cite book | author=Paul Halmos | authorlink=Paul Halmos | title=Naive set theory | series=The University Series in Undergraduate Mathematics | publisher=[[V