The fiXed point of a function, f is any value, X for which f X = X. A function may have any number of fiXed points from none (e.g. f X = X+1) to infinitely many (e.g. f X = X). The fiXed point combinator, written as either "fiX" or "Y" will return the fiXed point of a function. See also least fiXed point. (1995-04-13)