Theorem pm2.6 162

Description: Theorem *2.6 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.6	⊢ ((¬ φ → ψ) → ((φ → ψ) → ψ))

Proof of Theorem pm2.6

Step	Hyp	Ref	Expression
1		id 19	. 2 ⊢ ((¬ φ → ψ) → (¬ φ → ψ))
2		idd 21	. 2 ⊢ ((¬ φ → ψ) → (ψ → ψ))
3	1, 2	jad 154	1 ⊢ ((¬ φ → ψ) → ((φ → ψ) → ψ))

Syntax hints:  ¬ wn 3   → wi 4

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

This theorem is referenced by:  pm2.61  163