indirect proof

noun
1.
an argument for a proposition that shows its negation to be incompatible with a previously accepted or established premise.
Examples from the web for indirect proof
  • Devise ways to verify results, using counterexamples and indirect proof.
  • Devise ways to verify results, using counterexamples and informal indirect proof.
  • One stated that the transfusion data were flawed, but that secular trend data provided indirect proof of efficacy.
British Dictionary definitions for indirect proof

indirect proof

noun
1.
(logic, maths) proof of a conclusion by showing its negation to be self-contradictory; reductio ad absurdum Compare direct (sense 17)