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ZF (ZERMELO-FRAENKEL) SET THEORY
ZF Set Theory - start with the Axiom of Extensionality
Define basic set operations and relations
wpss

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Metamath Proof Explorer

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Syntax definition wpss

Description: Extend wff notation with proper subclass relation.

		Ref	Expression
	Assertion	wpss	wff 𝐴 ⊊ 𝐵