In particular, the set of all counterexamples contains a minimal element, the "minimal counterexample". The attempt to rebut an argument may involve generating a counterargument or finding a counterexample. The obvious way to disprove an impossibility conjecture by providing a single counterexample. Conjectures disproven through counterexample are sometimes referred to as "false conjectures" (cf. Allais presented his paradox as a counterexample to the independence axiom. No counterexample has been found to the conjecture. A ring species is a species with a counterexample to the transitivity of interbreeding. Then show that for any counterexample there is a still smaller counterexample, producing a contradiction. Marcel Duchamp's Fountain is the paradigmatic counterexample to aesthetic definitions of art. Proving that this is true (or finding a counterexample) remains an open problem. When the set is uncountable, this topology serves as a counterexample in many situations. In the absence of associativity, the sedenions provide a counterexample. By way of counterexample, a password authenticator is not a cryptographic authenticator. Such a counterexample is called a "Ramsey graph". Recently an explicit counterexample has been proposed in.