Theorem pm2.61 163

Description: Theorem *2.61 of [WhiteheadRussell] p. 107. Useful for eliminating an antecedent. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 22-Sep-2013.)

Assertion

Ref	Expression
pm2.61	⊢ ((φ → ψ) → ((¬ φ → ψ) → ψ))

Proof of Theorem pm2.61

Step	Hyp	Ref	Expression
1		pm2.6 162	. 2 ⊢ ((¬ φ → ψ) → ((φ → ψ) → ψ))
2	1	com12 27	1 ⊢ ((φ → ψ) → ((¬ φ → ψ) → ψ))

Syntax hints:  ¬ wn 3   → wi 4

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

This theorem is referenced by: (None)