Theorem pm4.55 515

Description: Theorem *4.55 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm4.55	|- ( -. ( -. ph /\ ps ) <-> ( ph \/ -. ps ) )

Proof of Theorem pm4.55

Step	Hyp	Ref	Expression
1		pm4.54 514	. . 3 |- ( ( -. ph /\ ps ) <-> -. ( ph \/ -. ps ) )
2	1	con2bii 347	. 2 |- ( ( ph \/ -. ps ) <-> -. ( -. ph /\ ps ) )
3	2	bicomi 214	1 |- ( -. ( -. ph /\ ps ) <-> ( ph \/ -. ps ) )

Syntax hints:   -. wn 3   <-> wb 196   \/ wo 383   /\ wa 384

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  df-an 386

This theorem is referenced by:  chrelat2i  29224  hlrelat2  34689  ifpnot23  37823