[[[3,3,
sub Ack {
   my($M, $N) = @_;
   return( $N + 1 )         if ($M == 0);
   return( Ack($M - 1, 1) ) if ($N == 0);
   Ack($M - 1, Ack($M, $N - 1));
}

return Ack($i,$j);
]]]


Function "Ack" (Ackermann's function) copied from Doug Bagley.