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Axiom ax-luk2 33555
Description: 2 of 3 axioms for propositional calculus due to Lukasiewicz. Copy of luk-2 1736 or pm2.18 125, but introduced as an axiom. The core idea behind this axiom is, that if something can be implied from both an antecedent, and separately from its negation, then the antecedent is irrelevant to the consequent, and can safely be dropped. This is perhaps better seen from the following slightly extended version (related to pm2.65 184):

((𝜑𝜑) → ((¬ 𝜑𝜑) → 𝜑)). (Contributed by Wolf Lammen, 17-Dec-2018.) (New usage is discouraged.)

Assertion
Ref Expression
ax-luk2 ((¬ 𝜑𝜑) → 𝜑)

Detailed syntax breakdown of Axiom ax-luk2
StepHypRef Expression
1 wph . . 3 wff 𝜑
21wn 3 . 2 wff ¬ 𝜑
32, 1, 1bj-0 32845 1 wff ((¬ 𝜑𝜑) → 𝜑)
Colors of variables: wff setvar class
This axiom is referenced by:  wl-pm2.18d  33561  wl-ax3  33568  wl-pm2.27  33570  wl-id  33578
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