Theorem pm4.25 501

Description: Theorem *4.25 of [WhiteheadRussell] p. 117. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm4.25	⊢ (φ ↔ (φ ∨ φ))

Proof of Theorem pm4.25

Step	Hyp	Ref	Expression
1		oridm 500	. 2 ⊢ ((φ ∨ φ) ↔ φ)
2	1	bicomi 193	1 ⊢ (φ ↔ (φ ∨ φ))

Syntax hints:   ↔ wb 176   ∨ 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)