Theorem eqtrid

Description: An equality transitivity deduction. (Contributed by NM, 21-Jun-1993)

	Ref	Expression
Hypotheses	eqtrid.1	|- A = B
	eqtrid.2	|- ( ph -> B = C )
Assertion	eqtrid	|- ( ph -> A = C )

Proof

Step	Hyp	Ref	Expression
1		eqtrid.1	|- A = B
2		eqtrid.2	|- ( ph -> B = C )
3	1	a1i	|- ( ph -> A = B )
4	3 2	eqtrd	|- ( ph -> A = C )