Theorem reubii

Description: Formula-building rule for restricted existential quantifier (inference form). (Contributed by NM, 22-Oct-1999)

	Ref	Expression
Hypothesis	reubii.1	|- ( ph <-> ps )
Assertion	reubii	|- ( E! x e. A ph <-> E! x e. A ps )

Proof

Step	Hyp	Ref	Expression
1		reubii.1	|- ( ph <-> ps )
2	1	a1i	|- ( x e. A -> ( ph <-> ps ) )
3	2	reubiia	|- ( E! x e. A ph <-> E! x e. A ps )