Theorem sbali

Description: Discard class substitution in a universal quantification when substituting the quantified variable, in inference form. (Contributed by Giovanni Mascellani, 27-May-2019)

	Ref	Expression
Hypothesis	sbali.1	|- A e. _V
Assertion	sbali	|- ( [. A / x ]. A. x ph <-> A. x ph )

Proof

Step	Hyp	Ref	Expression
1		sbali.1	|- A e. _V
2		nfa1	|- F/ x A. x ph
3	1 2	sbcgfi	|- ( [. A / x ]. A. x ph <-> A. x ph )