Metamath Proof Explorer


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