Theorem reubiia

Description: Formula-building rule for restricted existential quantifier (inference form). (Contributed by NM, 14-Nov-2004)

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

Proof

Step	Hyp	Ref	Expression
1		reubiia.1	|- ( x e. A -> ( ph <-> ps ) )
2	1	pm5.32i	|- ( ( x e. A /\ ph ) <-> ( x e. A /\ ps ) )
3	2	eubii	|- ( E! x ( x e. A /\ ph ) <-> E! x ( x e. A /\ ps ) )
4		df-reu	|- ( E! x e. A ph <-> E! x ( x e. A /\ ph ) )
5		df-reu	|- ( E! x e. A ps <-> E! x ( x e. A /\ ps ) )
6	3 4 5	3bitr4i	|- ( E! x e. A ph <-> E! x e. A ps )