Theorem pm2.13 407

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

Assertion

Ref	Expression
pm2.13	⊢ (φ ∨ ¬ ¬ ¬ φ)

Proof of Theorem pm2.13

Step	Hyp	Ref	Expression
1		notnot1 114	. 2 ⊢ (¬ φ → ¬ ¬ ¬ φ)
2	1	orri 365	1 ⊢ (φ ∨ ¬ ¬ ¬ φ)

Syntax hints:  ¬ wn 3   ∨ wo 357

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 177  df-or 359

This theorem is referenced by: (None)