for  $a (1 .. 2) { # a  has 2 levels:
 for  $t (1 .. 2) { # t has 2 levels:
  for  $g (1 .. 2) { # g has 2 levels:
   for  $c (1 .. 2) { # c has 2 levels: 

 $combi=sprintf($new_four,$a,$t,$g,$c,3-$a,3-$t,3-$g,3-$c); 
print"~$combi\n"; 
print $fh "~$combi\n";