Theorem pm5.19 668

Description: Theorem *5.19 of [WhiteheadRussell] p. 124.

Assertion

Ref	Expression
pm5.19	|- -. (ph <-> -. ph)

Proof of Theorem pm5.19

Step	Hyp	Ref	Expression
1		pm4.2 170	. 2 |- (ph <-> ph)
2		pm5.18 659	. 2 |- ((ph <-> ph) <-> -. (ph <-> -. ph))
3	1, 2	mpbi 189	1 |- -. (ph <-> -. ph)

Syntax hints:  -. wn 2   <-> wb 146

This theorem is referenced by:  ru 1934  axnul2 2703

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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