Theorem notnotnot 664

Description: Triple negation. (Contributed by Jim Kingdon, 28-Jul-2018.)

Assertion

Ref	Expression
notnotnot	⊢ (¬ ¬ ¬ 𝜑 ↔ ¬ 𝜑)

Proof of Theorem notnotnot

Step	Hyp	Ref	Expression
1		notnot 595	. . 3 ⊢ (𝜑 → ¬ ¬ 𝜑)
2	1	con3i 598	. 2 ⊢ (¬ ¬ ¬ 𝜑 → ¬ 𝜑)
3		notnot 595	. 2 ⊢ (¬ 𝜑 → ¬ ¬ ¬ 𝜑)
4	2, 3	impbii 125	1 ⊢ (¬ ¬ ¬ 𝜑 ↔ ¬ 𝜑)

Syntax hints:  ¬ wn 3   ↔ wb 104

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia2 106  ax-ia3 107  ax-in1 580  ax-in2 581

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  stabnot  779  testbitestn  862