[John Machin] > 2. Without a definition that refers only to to the input and output, > one would have to say that "interchange" implies "event" and so the > number of interchanges would depend on the sorting method.
As the dataset contains no duplicates, the parity will be the same irrespective of sorting method. > 3. Of what practical use (or even esoteric academic interest) is the > parity of the number of interchanges? I presume the goal is academic, determining whether a permutation is a member of the alternating group of even permutations (A4, A5, ...). For some problems, that is a useful invariant. For instance, iirc, the parity determines whether a given 15 puzzle arrangement is solvable. Raymond -- http://mail.python.org/mailman/listinfo/python-list
