Metamath Proof Explorer


Theorem bj-bialal

Description: When ph is substituted for ps , both sides express a form of nonfreeness. (Contributed by BJ, 20-Oct-2019)

Ref Expression
Assertion bj-bialal x x φ ψ x φ x ψ

Proof

Step Hyp Ref Expression
1 nfa1 x x φ
2 1 19.21 x x φ ψ x φ x ψ