Theorem simprim 142

Description: Simplification. Similar to Theorem *3.27 (Simp) of [WhiteheadRussell] p. 112. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 13-Nov-2012.)

Assertion

Ref	Expression
simprim	⊢ (¬ (φ → ¬ ψ) → ψ)

Proof of Theorem simprim

Step	Hyp	Ref	Expression
1		idd 21	. 2 ⊢ (φ → (ψ → ψ))
2	1	impi 140	1 ⊢ (¬ (φ → ¬ ψ) → ψ)

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:  impt  149  bi3  179  bi2  189