Metamath Proof Explorer

Theorem r19.28zv

Description: Restricted quantifier version of Theorem 19.28 of Margaris p. 90. It is valid only when the domain of quantification is not empty. (Contributed by NM, 19-Aug-2004)

Ref Expression
Assertion r19.28zv A x A φ ψ φ x A ψ


Step Hyp Ref Expression
1 nfv x φ
2 1 r19.28z A x A φ ψ φ x A ψ