Theorem axfrege58b

Description: If A. x ph is affirmed, [ y / x ] ph cannot be denied. Identical to stdpc4 . Justification for ax-frege58b . (Contributed by RP, 28-Mar-2020)

	Ref	Expression
Assertion	axfrege58b	⊢ ( ∀ 𝑥 𝜑 → [ 𝑦 / 𝑥 ] 𝜑 )

Proof

Step	Hyp	Ref	Expression
1		stdpc4	⊢ ( ∀ 𝑥 𝜑 → [ 𝑦 / 𝑥 ] 𝜑 )