Theorem zeo4

Description: An integer is even or odd but not both. With this representation of even and odd integers, this variant of zeo2 follows immediately from the principle of double negation, see notnotb . (Contributed by AV, 17-Jun-2021)

	Ref	Expression
Assertion	zeo4	⊢ ( 𝑁 ∈ ℤ → ( 2 ∥ 𝑁 ↔ ¬ ¬ 2 ∥ 𝑁 ) )

Proof

Step	Hyp	Ref	Expression
1		notnotb	⊢ ( 2 ∥ 𝑁 ↔ ¬ ¬ 2 ∥ 𝑁 )
2	1	a1i	⊢ ( 𝑁 ∈ ℤ → ( 2 ∥ 𝑁 ↔ ¬ ¬ 2 ∥ 𝑁 ) )