1. The problem statement, all variables and given/known data A person can either be a knight (always tells the truth) or a knave (always tells a lie). On an island with three persons (A, B and C), A tells "If I am a knight, then at least one of us is a knave". 2. Relevant equations Truth tables, logic rules. 3. The attempt at a solution Using the atoms P=A is a knight, Q=B is a knight, R=C is a knight, and the sentence P⟺P→(¬P∨¬Q∨¬R) I get the following truth table: How can I find if A is a knight or a knave from this table? My guess would be that he is a knave since it is not a tautology but I am really not sure. Thanks!