C:\usr\local\share>perl -MAlgorithm::Permute -e "my $p=Algorithm::Permute::->new([1..4],2); while(my @res=$p->next){print qq(@res\n)}"
2 1
1 2
3 2
2 3
3 1
1 3
4 2
2 4
4 3
3 4
4 1
1 4