Theorem bj-nnor 16774

Description: Double negation of a disjunction in terms of implication. (Contributed by BJ, 9-Oct-2019.)

Assertion

Ref	Expression
bj-nnor	⊢ (¬ ¬ (𝜑 ∨ 𝜓) ↔ (¬ 𝜑 → ¬ ¬ 𝜓))

Proof of Theorem bj-nnor

Step	Hyp	Ref	Expression
1		ioran 764	. . 3 ⊢ (¬ (𝜑 ∨ 𝜓) ↔ (¬ 𝜑 ∧ ¬ 𝜓))
2	1	notbii 678	. 2 ⊢ (¬ ¬ (𝜑 ∨ 𝜓) ↔ ¬ (¬ 𝜑 ∧ ¬ 𝜓))
3		imnan 701	. 2 ⊢ ((¬ 𝜑 → ¬ ¬ 𝜓) ↔ ¬ (¬ 𝜑 ∧ ¬ 𝜓))
4	2, 3	bitr4i 187	1 ⊢ (¬ ¬ (𝜑 ∨ 𝜓) ↔ (¬ 𝜑 → ¬ ¬ 𝜓))

This proof depends on syntax axioms:  ¬ wn 3   → wi 4   ∧ wa 104   ↔ wb 105   ∨ wo 720

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 623  ax-in2 624  ax-io 721

This proof depends on definitions:  df-bi 117

This theorem is used by:  bj-nndcALT  16798