method a(m n)
  if m=0 then
    return n-(-1);
  else
	if (0<m) then
		if (n=0) then
		    return a(m-1,1);
		else
    		return a(m-1,a(m,n-1));
		end;
	else
   		return a(m-1,a(m,n-1));
	end;		
  end;
end;