Knights and Knaves: Judy, Rupert, Frank, and Mallory

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knights knaves

On an island, every inhabitant is either a knight, who always tells the truth, or a knave, who always lies. You meet Judy, Rupert, Frank, and Mallory. Judy says: "I am a knave or Rupert is a knave." Frank says: "Rupert and Mallory are of different types." Mallory says: "Frank is a knave and I am a knight." The others say nothing. Who is a knight and who is a knave?

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Solution

Commit an attempt to unseal the proof. Write your answer — right or wrong, thinking it through is the point.

Once you've worked out who is who: how many of the 4 inhabitants are knaves? Answer with the number.

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