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I came across this puzzle a few days ago, it’s supposedly the most difficult logic puzzle in the world, made by a Harvard professor of psychology. I was unable to solve it (after several hours of scratching my head) and eventually had to concede defeat. I did however come across a very unconventional solution to the puzzle that is acceptable based on the criteria stipulated by the creator of the puzzle, as far as I can tell that is (not the Wikipedia solution). I am however unsure whether others will agree with this assertion or not. “Three gods A, B, and C are called, in no particular order, True, False, and Random. True always speaks truly, False always speaks falsely, but whether Random speaks truly or falsely is a completely random matter. Your task is to determine the identities of A, B, and C by asking three yes-no questions; each question must be put to exactly one god. The gods understand English, but will answer all questions in their own language, in which the words for yes and no are da and ja, in some order. You do not know which word means which. It could be that some god gets asked more than one question (and hence that some god is not asked any question at all). What the second question is, and to which god it is put, may depend on the answer to the first question. (And of course similarly for the third question.) Whether Random speaks truly or not should be thought of as depending on the flip of a coin hidden in his brain: if the coin comes down heads, he speaks truly; if tails, falsely”

N lamps are set in a circle, and for each integer M you have a tool that can toggle the state (on/off) of any set of M consecutive lamps. Find a possible N which satisfies the following statements: The sum of its digits is less than 10. By applying the tool for M=105 several times, we can toggle a single lamp. If we remove one lamp and start from a random initial setting for the remaining N-1 lamps, the probability that there exists a way to apply the tool for M=32 several times and switch all the lamps off is positive and less than 0.0011%.