Try this:

for my $seq1 ( 1 .. 5 ) {
    for my $seq2 ( 1 .. $seq1 - 1, $seq1 + 1 .. 5 ) {
        print "$seq1 : $seq2";
    }
}
;;
1 : 2
1 : 3
1 : 4
1 : 5
2 : 1
2 : 3
2 : 4
2 : 5
3 : 1
3 : 2
3 : 4
3 : 5
4 : 1
4 : 2
4 : 3
4 : 5
5 : 1
5 : 2
5 : 3
5 : 4
[download]

thanks! that's exactly what I needed!

You can try following algorithm:

• 1. compare seq 1 with seq 2 (create intersection 12).
• 2. compare seq 3 with intersection 12 (create intersection 13).
• 3. compare seq 4 with intersection 13 (create intersection 14)
• ...