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Metamath Proof Explorer

Theorem negnegd

Description: A number is equal to the negative of its negative. Theorem I.4 of Apostol p. 18. (Contributed by Mario Carneiro, 27-May-2016)

		Ref	Expression
	Hypothesis	negidd.1	$⊢ φ \to A \in ℂ$
	Assertion	negnegd	$⊢ φ \to - (- A) = A$

Step	Hyp	Ref	Expression
1		negidd.1	$⊢ φ \to A \in ℂ$
2		negneg	$⊢ A \in ℂ \to - (- A) = A$
3	1 2	syl	$⊢ φ \to - (- A) = A$