Theorem con4bii 521

Description: A contraposition inference.

Hypothesis

Ref	Expression
con4bii.1	|- (-. ph <-> -. ps)

Assertion

Ref	Expression
con4bii	|- (ph <-> ps)

Proof of Theorem con4bii

Step	Hyp	Ref	Expression
1		con4bii.1	. 2 |- (-. ph <-> -. ps)
2		pm4.11 520	. 2 |- ((ph <-> ps) <-> (-. ph <-> -. ps))
3	1, 2	mpbir 190	1 |- (ph <-> ps)

Syntax hints:  -. wn 2   <-> wb 146

This theorem is referenced by:  gencbval 1831  dfpss3 2124  eq0 2284  uni0b 2513

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-an 225

Copyright terms: Public domain