Theorem dfvd2

Description: Definition of a 2-hypothesis virtual deduction. (Contributed by Alan Sare, 14-Nov-2011) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	dfvd2	|- ( (. ph ,. ps ->. ch ). <-> ( ph -> ( ps -> ch ) ) )

Proof

Step	Hyp	Ref	Expression
1		df-vd2	|- ( (. ph ,. ps ->. ch ). <-> ( ( ph /\ ps ) -> ch ) )
2		impexp	|- ( ( ( ph /\ ps ) -> ch ) <-> ( ph -> ( ps -> ch ) ) )
3	1 2	bitri	|- ( (. ph ,. ps ->. ch ). <-> ( ph -> ( ps -> ch ) ) )