Theorem negeq

Description: Equality theorem for negatives. (Contributed by NM, 10-Feb-1995)

	Ref	Expression
Assertion	negeq	$$⊢A=B\to -A=-B$$

Proof

Step	Hyp	Ref	Expression
1		oveq2	$$⊢A=B\to 0-A=0-B$$
2		df-neg	$$⊢-A=0-A$$
3		df-neg	$$⊢-B=0-B$$
4	1 2 3	3eqtr4g	$$⊢A=B\to -A=-B$$