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 ∈ ℂ
2	1 1	mul2negi	⊢ ( - 1 · - 1 ) = ( 1 · 1 )
3		1t1e1	⊢ ( 1 · 1 ) = 1
4	2 3	eqtri	⊢ ( - 1 · - 1 ) = 1