Theorem pm4.55 310

Description: Theorem *4.55 of [WhiteheadRussell] p. 120.

Assertion

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

Proof of Theorem pm4.55

Step	Hyp	Ref	Expression
1		pm4.54 309	. . 3 |- ((-. ph /\ ps) <-> -. (ph \/ -. ps))
2	1	con2bii 221	. 2 |- ((ph \/ -. ps) <-> -. (-. ph /\ ps))
3	2	bicomi 172	1 |- (-. (-. ph /\ ps) <-> (ph \/ -. ps))

Syntax hints:  -. wn 2   <-> wb 146   \/ wo 222   /\ wa 223

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  df-an 225

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