P91 - Knight's tour.

Another famous problem is this one: How can a knight jump on an N×Nchessboard in such a way that it visits every square exactly once?

Hints: Represent the squares by pairs of their coordinates of the form (X, Y), where both X and Y are integers between 1 and N. (Alternately, define a Point class for the same purpose.) Write a function jumps(N, (X, Y)) to list the squares that a knight can jump to from (X, Y) on a N×N chessboard. And finally, represent the solution of our problem as a list of knight positions (the knight's tour).

It might be nice to find more than one tour, but a computer will take a long time trying to find them all at once. Can you make a lazy list that only calculates the tours as needed?

Can you find only "closed tours", where the knight can jump from its final position back to its starting position?