Theorem r19.37zv

Description: Restricted quantifier version of Theorem 19.37 of Margaris p. 90. It is valid only when the domain of quantification is not empty. (Contributed by Paul Chapman, 8-Oct-2007)

	Ref	Expression
Assertion	r19.37zv	$$⊢A\ne \varnothing \to \left(\exists x\in A\left(\phi \to \psi \right)\leftrightarrow \left(\phi \to \exists x\in A\psi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		r19.3rzv	$$⊢A\ne \varnothing \to \left(\phi \leftrightarrow \forall x\in A\phi \right)$$
2	1	imbi1d	$$⊢A\ne \varnothing \to \left(\left(\phi \to \exists x\in A\psi \right)\leftrightarrow \left(\forall x\in A\phi \to \exists x\in A\psi \right)\right)$$
3		r19.35	$$⊢\exists x\in A\left(\phi \to \psi \right)\leftrightarrow \left(\forall x\in A\phi \to \exists x\in A\psi \right)$$
4	2 3	syl6rbbr	$$⊢A\ne \varnothing \to \left(\exists x\in A\left(\phi \to \psi \right)\leftrightarrow \left(\phi \to \exists x\in A\psi \right)\right)$$