my %seen;
for each combination @c: #however you do this with Math::Combinatorics
  my $wanted = 1;
CHECK:
  for my $i (0..$#c) {
    for my $j ($i+1..$#c) {
      if ($seen{$c[$i],$c[$j]} || $seen{$c[$j],$c[$i]}) {
        $wanted = 0;
        last CHECK;
      }
  }
  next unless $wanted;
  # emit combination here
  # go through pairs again to mark them as seen
  for my $i (0..$#c) {
    for my $j ($i+1..$#c) {
      $seen{$c[$i],$c[$j]} = 1;
      $seen{$c[$j],$c[$i]} = 1;
    }
  }
}