-module(ackermann).
-export([ackermann/2]).

ackermann(0, N) ->
  N+1;
ackermann(M, 0) ->
  ackermann(M-1, 1);
ackermann(M, N) when M > 0 andalso N > 0 ->
  ackermann(M-1, ackermann(M, N-1)).