public void TestAllPermutations()
{
var r = Permutation.AllPermutations_S1(new[] { 1, 2, 3, 4 });
Assert.AreEqual(r.Count, 4 * 3 * 2);
r = Permutation.AllPermutations_S2(new[] { 1, 2, 3, 4, 5 });
Assert.AreEqual(r.Count, 5 * 4 * 3 * 2);
}