Theorem pm2.01 160

Description: Reductio ad absurdum. Theorem *2.01 of [WhiteheadRussell] p. 100. (Contributed by NM, 18-Aug-1993.) (Proof shortened by O'Cat, 21-Nov-2008.) (Proof shortened by Wolf Lammen, 31-Oct-2012.)

Assertion

Ref	Expression
pm2.01	⊢ ((φ → ¬ φ) → ¬ φ)

Proof of Theorem pm2.01

Step	Hyp	Ref	Expression
1		id 19	. 2 ⊢ (¬ φ → ¬ φ)
2	1, 1	ja 153	1 ⊢ ((φ → ¬ φ) → ¬ φ)

Syntax hints:  ¬ wn 3   → wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem is referenced by:  bijust  175  pm4.8  354