Theorem csbeq1a

Description: Equality theorem for proper substitution into a class. (Contributed by NM, 10-Nov-2005)

	Ref	Expression
Assertion	csbeq1a	$$⊢x=A\to B=⦋A/x⦌B$$

Proof

Step	Hyp	Ref	Expression
1		csbid	$$⊢⦋x/x⦌B=B$$
2		csbeq1	$$⊢x=A\to ⦋x/x⦌B=⦋A/x⦌B$$
3	1 2	eqtr3id	$$⊢x=A\to B=⦋A/x⦌B$$