Theorem sylnbir 669

Description: A mixed syllogism inference from a biconditional and an implication. (Contributed by Wolf Lammen, 16-Dec-2013.)

Hypotheses

Ref	Expression
sylnbir.1	|- ( ps <-> ph )
sylnbir.2	|- ( -. ps -> ch )

Assertion

Ref	Expression
sylnbir	|- ( -. ph -> ch )

Proof of Theorem sylnbir

Step	Hyp	Ref	Expression
1		sylnbir.1	. . 3 |- ( ps <-> ph )
2	1	bicomi 131	. 2 |- ( ph <-> ps )
3		sylnbir.2	. 2 |- ( -. ps -> ch )
4	2, 3	sylnbi 668	1 |- ( -. ph -> ch )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 104

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-in1 604  ax-in2 605

This theorem depends on definitions:  df-bi 116

This theorem is referenced by: (None)