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Metamath Proof Explorer

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 )