Theorem equtrr

Description: A transitive law for equality. Lemma L17 in Megill p. 446 (p. 14 of the preprint). (Contributed by NM, 23-Aug-1993)

	Ref	Expression
Assertion	equtrr	$$⊢x=y\to \left(z=x\to z=y\right)$$

Proof

Step	Hyp	Ref	Expression
1		equtr	$$⊢z=x\to \left(x=y\to z=y\right)$$
2	1	com12	$$⊢x=y\to \left(z=x\to z=y\right)$$