Theorem pm2.13

Description: Theorem *2.13 of WhiteheadRussell p. 101. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm2.13	⊢ ( 𝜑 ∨ ¬ ¬ ¬ 𝜑 )

Proof

Step	Hyp	Ref	Expression
1		notnot	⊢ ( ¬ 𝜑 → ¬ ¬ ¬ 𝜑 )
2	1	orri	⊢ ( 𝜑 ∨ ¬ ¬ ¬ 𝜑 )