Knights and Knaves: Sybil, Frank, Mallory, and Bob

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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 Sybil, Frank, Mallory, and Bob. Sybil says: "Mallory is a knight and Bob is a knave." Frank says: "Bob is a knave and Sybil is a knave." Bob says: "I am a knave and Sybil is 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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