Theorem pm2.67 392

Description: Theorem *2.67 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.67	⊢ (((φ ∨ ψ) → ψ) → (φ → ψ))

Proof of Theorem pm2.67

Step	Hyp	Ref	Expression
1		pm2.67-2 391	1 ⊢ (((φ ∨ ψ) → ψ) → (φ → ψ))

This proof depends on syntax axioms:   → wi 4   ∨ wo 357

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

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

This theorem is used by: (None)