Theorem pm1.2 499

Description: Axiom *1.2 of [WhiteheadRussell] p. 96, which they call "Taut". (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm1.2	⊢ ((φ ∨ φ) → φ)

Proof of Theorem pm1.2

Step	Hyp	Ref	Expression
1		id 19	. 2 ⊢ (φ → φ)
2	1, 1	jaoi 368	1 ⊢ ((φ ∨ φ) → φ)

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:  oridm  500  rb-ax4  1520