Theorem 3eqtrri

Description: An inference from three chained equalities. (Contributed by NM, 3-Aug-2006) (Proof shortened by Andrew Salmon, 25-May-2011)

	Ref	Expression
Hypotheses	3eqtri.1	$$⊢A=B$$
	3eqtri.2	$$⊢B=C$$
	3eqtri.3	$$⊢C=D$$
Assertion	3eqtrri	$$⊢D=A$$

Proof

Step	Hyp	Ref	Expression
1		3eqtri.1	$$⊢A=B$$
2		3eqtri.2	$$⊢B=C$$
3		3eqtri.3	$$⊢C=D$$
4	1 2	eqtri	$$⊢A=C$$
5	4 3	eqtr2i	$$⊢D=A$$