Theorem necon2i

Description: Contrapositive inference for inequality. (Contributed by NM, 18-Mar-2007)

	Ref	Expression
Hypothesis	necon2i.1	$$⊢A=B\to C\ne D$$
Assertion	necon2i	$$⊢C=D\to A\ne B$$

Proof

Step	Hyp	Ref	Expression
1		necon2i.1	$$⊢A=B\to C\ne D$$
2	1	neneqd	$$⊢A=B\to \neg C=D$$
3	2	necon2ai	$$⊢C=D\to A\ne B$$