Theorem simprim

Description: Simplification. Similar to Theorem *3.27 (Simp) of WhiteheadRussell p. 112. (Contributed by NM, 3-Jan-1993) (Proof shortened by Wolf Lammen, 13-Nov-2012)

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

Proof

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