permutations

1 import std.algorithm.comparison : equal;
2 import std.range : iota;
3 assert(equal!equal(iota(3).permutations,
4     [[0, 1, 2],
5      [1, 0, 2],
6      [2, 0, 1],
7      [0, 2, 1],
8      [1, 2, 0],
9      [2, 1, 0]]));