My last adventure on this island during that particular visit was a curious one. I met a native who said, "This is not the first time I have said what I am now saying."(Source: To Mock a Mockingbird and Other Logic Puzzles: Including an Amazing Adventure in Combinatory Logic by Raymond Smullyan)
Was the native a knight or a knave?
If the native was a knight, then he has said in the past "This is not the first time I have said what I am now saying" and because he is a knight, that is true. Then he has said the same thing at another, earlier time, and it was equally true then. This ultimately leads to infinite regress. I am not going to offer an opinion on the philosophical issues of infinity here but, on the assumption that knights and knaves are finite beings, the native was definitely a knave. (This is also the answer given in the end-of-chapter solutions, for essentially the same reason.)
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