Function BTA($a,$b)
   dim $x,$,$s,$y
   $b = $a,$b,0
   while $b[0] + $b[1]
      $s=3
      for $a=0 to 2
         $y = $b[$a]
         $x= right($y,2)
         $b[$a]=left($y,len($y)-1-($x<0))
         $s = $s + $x mod 2
      next
      $a=0,1,-1,0,1,-1,0,-1,-1,0,0,0,1,1
      $ =  "" + $a[$s] + $
      $b[2] = $a[$s+7]
   loop
   
   $ = "0" + $b[2] + $
   do
      $ = substr($,2)
   until left($,1)<>0 or len($)<2
   $BTA=$
EndFunction