Theorem 19.28v

Description: Version of 19.28 with a disjoint variable condition, requiring fewer axioms. (Contributed by NM, 25-Mar-2004)

	Ref	Expression
Assertion	19.28v	|- ( A. x ( ph /\ ps ) <-> ( ph /\ A. x ps ) )

Proof

Step	Hyp	Ref	Expression
1		19.26	|- ( A. x ( ph /\ ps ) <-> ( A. x ph /\ A. x ps ) )
2		19.3v	|- ( A. x ph <-> ph )
3	2	anbi1i	|- ( ( A. x ph /\ A. x ps ) <-> ( ph /\ A. x ps ) )
4	1 3	bitri	|- ( A. x ( ph /\ ps ) <-> ( ph /\ A. x ps ) )