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Metamath Proof Explorer

Theorem pm2.21ddALT

Description: Alternate proof of pm2.21dd . (Contributed by Mario Carneiro, 9-Feb-2017) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Hypotheses	pm2.21ddALT.1	\|- ( ph -> ps )
	pm2.21ddALT.2	\|- ( ph -> -. ps )
Assertion	pm2.21ddALT	\|- ( ph -> ch )

Proof

Step	Hyp	Ref	Expression
1		pm2.21ddALT.1	\|- ( ph -> ps )
2		pm2.21ddALT.2	\|- ( ph -> -. ps )
3	2	pm2.21d	\|- ( ph -> ( ps -> ch ) )
4	1 3	mpd	\|- ( ph -> ch )