Theorem dfnot 1559

Description: Given falsum ⊥, we can define the negation of a wff 𝜑 as the statement that ⊥ follows from assuming 𝜑. (Contributed by Mario Carneiro, 9-Feb-2017.) (Proof shortened by Wolf Lammen, 21-Jul-2019.)

Assertion

Ref	Expression
dfnot	⊢ (¬ 𝜑 ↔ (𝜑 → ⊥))

Proof of Theorem dfnot

Step	Hyp	Ref	Expression
1		fal 1554	. 2 ⊢ ¬ ⊥
2		mtt 364	. 2 ⊢ (¬ ⊥ → (¬ 𝜑 ↔ (𝜑 → ⊥)))
3	1, 2	ax-mp 5	1 ⊢ (¬ 𝜑 ↔ (𝜑 → ⊥))

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 206  ⊥wfal 1552

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 207  df-tru 1543  df-fal 1553

This theorem is referenced by:  inegd  1560  ralf0  4494  bj-godellob  36628  irrdifflemf  37348