# null.
$q[1] eq $q[0] ||                                     !$graph{$q [0]}{$q [1]}
$q[2] eq $q[0] || $q[2] eq $q[1] ||                   !$graph{$q [1]}{$q [2]}
$q[3] eq $q[0] || $q[3] eq $q[1] || $q[3] eq $q[2] || !$graph{$q [2]}{$q [3]}