The '''empty set''' is the unique set that contains no element and is a subset of every other set. Its existence is postulated by the [[Axiom of empty set]] in the axioms of [[Zermelo–Fraenkel set theory]]. Note that the empty set is not a subset of the empty set in Zermelo–Fraenkel set theory.
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The '''empty set''' is the unique set that contains no element and is a subset of every other set. Its existence is postulated by the [[Axiom of empty set]] in the axioms of [[Zermelo–Fraenkel set theory]]. Note that the empty set is not a subset of the empty set in Zermelo–Fraenkel [[set theory.]]