Theorem pm2.521 103

Description: Theorem *2.521 of [WhiteheadRussell] p. 107.

Assertion

Ref	Expression
pm2.521	|- (-. (ph -> ps) -> (ps -> ph))

Proof of Theorem pm2.521

Step	Hyp	Ref	Expression
1		pm2.52 102	. 2 |- (-. (ph -> ps) -> (-. ph -> -. ps))
2	1	a3d 75	1 |- (-. (ph -> ps) -> (ps -> ph))

Syntax hints:  -. wn 2   -> wi 3

This theorem is referenced by:  pm5.13 666

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7

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