Function A($)
   Dim $s,$f
   $a = 0
   If $ > 3&$ < 7&($^)+($<4) = 16
      While $
         $a = Right($,1)
         $s = $s+$f*(-9*(4 < $a)+$a)+$a
         $ = Left($,~)
         $f = 1-$f
         If $s mod 10 $a = 0
EndFunction