Theorem pm2.4 558

Description: Theorem *2.4 of [WhiteheadRussell] p. 106. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.4	⊢ ((φ ∨ (φ ∨ ψ)) → (φ ∨ ψ))

Proof of Theorem pm2.4

Step	Hyp	Ref	Expression
1		orc 374	. 2 ⊢ (φ → (φ ∨ ψ))
2		id 19	. 2 ⊢ ((φ ∨ ψ) → (φ ∨ ψ))
3	1, 2	jaoi 368	1 ⊢ ((φ ∨ (φ ∨ 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: (None)