Theorem csbconstgi

Description: The proper substitution of a class for a variable in another variable does not modify it, in inference form. (Contributed by Giovanni Mascellani, 30-May-2019)

	Ref	Expression
Hypothesis	csbconstgi.1	$$⊢A\in \mathrm{V}$$
Assertion	csbconstgi	$$⊢⦋A/x⦌y=y$$

Proof

Step	Hyp	Ref	Expression
1		csbconstgi.1	$$⊢A\in \mathrm{V}$$
2		csbconstg	$$⊢A\in \mathrm{V}\to ⦋A/x⦌y=y$$
3	1 2	ax-mp	$$⊢⦋A/x⦌y=y$$