Theorem neg1mulneg1e1

Description: -u 1 x. -u 1 is 1. (Contributed by David A. Wheeler, 8-Dec-2018)

	Ref	Expression
Assertion	neg1mulneg1e1	$$⊢-1-1=1$$

Proof

Step	Hyp	Ref	Expression
1		ax-1cn	$$⊢1\in ℂ$$
2	1 1	mul2negi	$$⊢-1-1=1\cdot 1$$
3		1t1e1	$$⊢1\cdot 1=1$$
4	2 3	eqtri	$$⊢-1-1=1$$