Theorem elpwOLD

Description: Obsolete proof of elpw as of 31-Dec-2023. (Proof modification is discouraged.) (New usage is discouraged.) (Contributed by NM, 31-Dec-1993)

	Ref	Expression
Hypothesis	elpwOLD.1	|- A e. _V
Assertion	elpwOLD	|- ( A e. ~P B <-> A C_ B )

Proof

Step	Hyp	Ref	Expression
1		elpwOLD.1	|- A e. _V
2		sseq1	|- ( x = A -> ( x C_ B <-> A C_ B ) )
3		df-pw	|- ~P B = { x | x C_ B }
4	1 2 3	elab2	|- ( A e. ~P B <-> A C_ B )