Theorem dfxor4 37077

Description: Express exclusive-or in terms of implication and negation. Statement in [Frege1879] p. 12. (Contributed by RP, 14-Apr-2020.)

Assertion

Ref	Expression
dfxor4	⊢ ((𝜑 ⊻ 𝜓) ↔ ¬ ((¬ 𝜑 → 𝜓) → ¬ (𝜑 → ¬ 𝜓)))

Proof of Theorem dfxor4

Step	Hyp	Ref	Expression
1		xor2 1462	. 2 ⊢ ((𝜑 ⊻ 𝜓) ↔ ((𝜑 ∨ 𝜓) ∧ ¬ (𝜑 ∧ 𝜓)))
2		df-or 384	. . 3 ⊢ ((𝜑 ∨ 𝜓) ↔ (¬ 𝜑 → 𝜓))
3		imnan 437	. . . 4 ⊢ ((𝜑 → ¬ 𝜓) ↔ ¬ (𝜑 ∧ 𝜓))
4	3	bicomi 213	. . 3 ⊢ (¬ (𝜑 ∧ 𝜓) ↔ (𝜑 → ¬ 𝜓))
5	2, 4	anbi12i 729	. 2 ⊢ (((𝜑 ∨ 𝜓) ∧ ¬ (𝜑 ∧ 𝜓)) ↔ ((¬ 𝜑 → 𝜓) ∧ (𝜑 → ¬ 𝜓)))
6		df-an 385	. 2 ⊢ (((¬ 𝜑 → 𝜓) ∧ (𝜑 → ¬ 𝜓)) ↔ ¬ ((¬ 𝜑 → 𝜓) → ¬ (𝜑 → ¬ 𝜓)))
7	1, 5, 6	3bitri 285	1 ⊢ ((𝜑 ⊻ 𝜓) ↔ ¬ ((¬ 𝜑 → 𝜓) → ¬ (𝜑 → ¬ 𝜓)))

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 195   ∨ wo 382   ∧ wa 383   ⊻ wxo 1456

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

This theorem depends on definitions:  df-bi 196  df-or 384  df-an 385  df-xor 1457

This theorem is referenced by:  dfxor5  37078