Theorem pm2.26 657

Description: Theorem *2.26 of [WhiteheadRussell] p. 104.

Assertion

Ref	Expression
pm2.26	|- (-. ph \/ ((ph -> ps) -> ps))

Proof of Theorem pm2.26

Step	Hyp	Ref	Expression
1		nega 84	. . . 4 |- (-. -. ph -> ph)
2	1	imim1i 16	. . 3 |- ((ph -> ps) -> (-. -. ph -> ps))
3	2	com12 11	. 2 |- (-. -. ph -> ((ph -> ps) -> ps))
4	3	orri 231	1 |- (-. ph \/ ((ph -> ps) -> ps))

Syntax hints:  -. wn 2   -> wi 3   \/ wo 222

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

This theorem depends on definitions:  df-bi 147  df-or 224

Copyright terms: Public domain