Theorem pm2.25 393

Description: Theorem *2.25 of [WhiteheadRussell] p. 104. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.25	⊢ (φ ∨ ((φ ∨ ψ) → ψ))

Proof of Theorem pm2.25

Step	Hyp	Ref	Expression
1		orel1 371	. 2 ⊢ (¬ φ → ((φ ∨ ψ) → ψ))
2	1	orri 365	1 ⊢ (φ ∨ ((φ ∨ ψ) → 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: (None)