counter-example
Finkel, Dan. (2020). Counterexamples. In S. Kohli (Ed.), Math Circle Activity Database. American Institute of Mathematics. https://mathcircles.org/activity/counterexamples/

Counterexamples

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Math Circles:
What can you do with a paperclip? What can you do with a grid? Answers to these questions lead participants to explore their own conjectures. This professional development session will help everyone turn their classroom into a Thinking Classroom, where students use Conjectures and Counterexamples to power genuine mathematical experiences. This session is suitable for all ages, math circles and classrooms.

Activity Guide

Math for Love has a website that includes free lessons including this one on Counterexamples!