Theorem negnegi

Description: A number is equal to the negative of its negative. Theorem I.4 of Apostol p. 18. (Contributed by NM, 8-Feb-1995) (Proof shortened by Andrew Salmon, 22-Oct-2011)

	Ref	Expression
Hypothesis	negidi.1	|- A e. CC
Assertion	negnegi	|- -u -u A = A

Proof

Step	Hyp	Ref	Expression
1		negidi.1	|- A e. CC
2		negneg	|- ( A e. CC -> -u -u A = A )
3	1 2	ax-mp	|- -u -u A = A