Theorem or12 756

Description: Swap two disjuncts. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 14-Nov-2012.)

Assertion

Ref	Expression
or12	|- ( ( ph \/ ( ps \/ ch ) ) <-> ( ps \/ ( ph \/ ch ) ) )

Proof of Theorem or12

Step	Hyp	Ref	Expression
1		pm1.5 755	. 2 |- ( ( ph \/ ( ps \/ ch ) ) -> ( ps \/ ( ph \/ ch ) ) )
2		pm1.5 755	. 2 |- ( ( ps \/ ( ph \/ ch ) ) -> ( ph \/ ( ps \/ ch ) ) )
3	1, 2	impbii 125	1 |- ( ( ph \/ ( ps \/ ch ) ) <-> ( ps \/ ( ph \/ ch ) ) )

Syntax hints:   <-> wb 104   \/ wo 698

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 699

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  orass  757  or32  760  or4  761