Theorem sylnbi 297

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

Hypotheses

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

Assertion

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

Proof of Theorem sylnbi

Step	Hyp	Ref	Expression
1		sylnbi.1	. . 3 |- (ph <-> ps)
2	1	notbii 287	. 2 |- (-. ph <-> -. ps)
3		sylnbi.2	. 2 |- (-. ps -> ch)
4	2, 3	sylbi 187	1 |- (-. ph -> ch)

Syntax hints:  -. wn 3   -> wi 4   <-> wb 176

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 177

This theorem is referenced by:  sylnbir  298  reuun2  3538  iotanul  4354  ndmfv  5349  ndmovcom  5617  fvfullfun  5864