Theorem pm5.11 854

Description: Theorem *5.11 of [WhiteheadRussell] p. 123. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm5.11	⊢ ((φ → ψ) ∨ (¬ φ → ψ))

Proof of Theorem pm5.11

Step	Hyp	Ref	Expression
1		pm2.5 144	. 2 ⊢ (¬ (φ → ψ) → (¬ φ → ψ))
2	1	orri 365	1 ⊢ ((φ → ψ) ∨ (¬ φ → ψ))

Syntax hints:  ¬ wn 3   → wi 4   ∨ 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)