function s($a)
   dim $,$i,$c,$n,$t
   $=' '
   for $n = 1-$a to 0
      $ = Wa + $ + aB
   next
   $ = split($,a)

   for $i = -$a to $a
      $n=-$n
      for $c=$n*($a-abs($i)) to -$c step -2*$n
         $[ascan($,' ')] = $[$c+$a]
         $[$c+$a]=' '
         $t=$t+join($,'')
         $s=split($t,a)
         $t=$t+a
endfunction