Tom found a counterexample which disproved Mary's assumption.

Inability to disprove a theory does not mean it is right.

All you need is one counterexample to disprove a theory.

A good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation.

A disproven principle. If A = B and B = C, then C = A. Is this true? Maybe. On Tatoeba C can be different from A.

Japan disproved phony accusations of computer chip dumping.

Science has disproven many cultural assumptions.