Theorem pm2.49 390

Description: Theorem *2.49 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.49	⊢ (¬ (φ ∨ ψ) → (¬ φ ∨ ¬ ψ))

Proof of Theorem pm2.49

Step	Hyp	Ref	Expression
1		pm2.46 387	. 2 ⊢ (¬ (φ ∨ ψ) → ¬ ψ)
2	1	olcd 382	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)