Proof by contradiction / counterexample construction

[305/34%]

Subtopics

Constructing examples with prescribed properties[131/21%]
Prove or disprove (deciding whether a statement holds)[94/53%]
Verifying a given counterexample[39/26%]
Necessity of hypotheses (a theorem fails without them)[26/31%]
Showing that a converse is false[9/67%]
Proof by contradiction and nonexistence proofs[7/71%]