Theorem mtpor 1420

Description: Modus tollendo ponens (inclusive-or version), aka disjunctive syllogism. This is similar to mtpxor 1421, one of the five original "indemonstrables" in Stoic logic. However, in Stoic logic this rule used exclusive-or, while the name modus tollendo ponens often refers to a variant of the rule that uses inclusive-or instead. The rule says, "if 𝜑 is not true, and 𝜑 or 𝜓 (or both) are true, then 𝜓 must be true". An alternate phrasing is, "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth". -- Sherlock Holmes (Sir Arthur Conan Doyle, 1890: The Sign of the Four, ch. 6). (Contributed by David A. Wheeler, 3-Jul-2016.) (Proof shortened by Wolf Lammen, 11-Nov-2017.)

Hypotheses

Ref	Expression
mtpor.min	⊢ ¬ 𝜑
mtpor.max	⊢ (𝜑 ∨ 𝜓)

Assertion

Ref	Expression
mtpor	⊢ 𝜓

Proof of Theorem mtpor

Step	Hyp	Ref	Expression
1		mtpor.min	. 2 ⊢ ¬ 𝜑
2		mtpor.max	. . 3 ⊢ (𝜑 ∨ 𝜓)
3	2	ori 718	. 2 ⊢ (¬ 𝜑 → 𝜓)
4	1, 3	ax-mp 5	1 ⊢ 𝜓

Syntax hints:  ¬ wn 3   ∨ wo 703

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in2 610  ax-io 704

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  mtpxor  1421  ordtriexmid  4505