for my $a (0, 1) {
  for my $b (0, 1) {
    print "c1 : $a, $b, ", c1($a, $b), "\n";
    print "c2 : $a, $b, ", c2($a, $b), "\n";
  }
}

sub c1 {
  my ($a, $b) = @_;
  $a and not $b
}

sub c2 {
  my ($a, $b) = @_;
  return $a and not $b
}