Theorem expi 161

Description: An exportation inference. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Mel L. O'Cat, 28-Nov-2008.)

Hypothesis

Ref	Expression
expi.1	|- ( -. ( ph -> -. ps ) -> ch )

Assertion

Ref	Expression
expi	|- ( ph -> ( ps -> ch ) )

Proof of Theorem expi

Step	Hyp	Ref	Expression
1		pm3.2im 157	. 2 |- ( ph -> ( ps -> -. ( ph -> -. ps ) ) )
2		expi.1	. 2 |- ( -. ( ph -> -. ps ) -> ch )
3	1, 2	syl6 35	1 |- ( ph -> ( ps -> ch ) )

Syntax hints:   -. wn 3   -> wi 4

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

This theorem is referenced by:  impbi  198  imbi12  336  ex  450