Theorem sseqtrri

Description: Substitution of equality into a subclass relationship. (Contributed by NM, 4-Apr-1995)

	Ref	Expression
Hypotheses	sseqtrri.1	|- A C_ B
	sseqtrri.2	|- C = B
Assertion	sseqtrri	|- A C_ C

Proof

Step	Hyp	Ref	Expression
1		sseqtrri.1	|- A C_ B
2		sseqtrri.2	|- C = B
3	2	eqcomi	|- B = C
4	1 3	sseqtri	|- A C_ C