Theorem impexp

Description: Import-export theorem. Part of Theorem *4.87 of WhiteheadRussell p. 122. (Contributed by NM, 10-Jan-1993) (Proof shortened by Wolf Lammen, 24-Mar-2013)

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

Proof

Step	Hyp	Ref	Expression
1		pm3.3	|- ( ( ( ph /\ ps ) -> ch ) -> ( ph -> ( ps -> ch ) ) )
2		pm3.31	|- ( ( ph -> ( ps -> ch ) ) -> ( ( ph /\ ps ) -> ch ) )
3	1 2	impbii	|- ( ( ( ph /\ ps ) -> ch ) <-> ( ph -> ( ps -> ch ) ) )