Jay, Kay & ElleAll games Counterexample!

Claim Investigation Bureau

Counterexample!

One case can change the answer.

Read each claim closely. Check its domain, test its conditions, and decide what the evidence really shows.

Investigator’s field guide

Claims and evidence

Always

Every permitted case satisfies the claim. A proof must cover them all.

Sometimes

You need one true case and one false case.

Never

No permitted case satisfies the claim.

Counterexample

One permitted case that shows an “always” claim is false.

Domain

The complete collection of cases the claim is about.

Proof

A reason that explains why every permitted case must work—not just a list of examples.

Settings

Reset progress?

This resets completed case files. Your Casebook and settings stay safe.

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