Theorem pm5.19 732

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		biid 187	. 2 |- (ph <-> ph)
2		pm5.18 722	. 2 |- ((ph <-> ph) <-> -. (ph <-> -. ph))
3	1, 2	mpbi 206	1 |- -. (ph <-> -. ph)

Syntax hints:  -. wn 2   <-> wb 163

This theorem is referenced by:  ru 2451  axnulALT 3443  bisym1 14243  rusbcALT 16410  compne 16417

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 164  df-an 242

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