Theorem pm2.68 399

Description: Theorem *2.68 of [WhiteheadRussell] p. 108. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.68	⊢ (((φ → ψ) → ψ) → (φ ∨ ψ))

Proof of Theorem pm2.68

Step	Hyp	Ref	Expression
1		jarl 155	. 2 ⊢ (((φ → ψ) → ψ) → (¬ φ → ψ))
2	1	orrd 367	1 ⊢ (((φ → ψ) → ψ) → (φ ∨ ψ))

Syntax hints:   → 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:  dfor2  400