Theorem pm4.66 436

Description: Theorem *4.66 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm4.66	|- ( ( -. ph -> -. ps ) <-> ( ph \/ -. ps ) )

Proof of Theorem pm4.66

Step	Hyp	Ref	Expression
1		pm4.64 387	1 |- ( ( -. ph -> -. ps ) <-> ( ph \/ -. ps ) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 196   \/ wo 383

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 197  df-or 385

This theorem is referenced by:  pm4.54  514  ifpim123g  37845  hirstL-ax3  41059