A counterexample is a specific case or example that disproves a statement or hypothesis. In logic and mathematics, if a general claim or assertion is made, a counterexample serves to show that the claim is not universally true by providing just one instance where it fails. For example, consider the statement: "All birds can fly." A counterexample to this statement would be a flightless bird, such as an ostrich or a penguin.
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A counterexample is one instance satisfying a claim’s hypotheses but not its conclusion, and therefore disproves the universal claim.