Theorem pm5.12 855

Description: Theorem *5.12 of [WhiteheadRussell] p. 123. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm5.12	⊢ ((φ → ψ) ∨ (φ → ¬ ψ))

Proof of Theorem pm5.12

Step	Hyp	Ref	Expression
1		pm2.51 145	. 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-1 5  ax-2 6  ax-3 7  ax-mp 8

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

This theorem is referenced by: (None)