function b = empty_fsa(M)
% does L(M) = \emptyset? i.e., does M accept any strings?

% actually, we achieve this by removing the unreachable states
b = isempty(M.F);

return

% everything below is included for info. only


% this is simple to resolve:
% is there a path from M.q0 to one of M.F?

nQ = length(M.Q);
% we only need to consider paths of length nQ-1

t = 1; b = 1;
Qt = M.q0;
while ((t<nQ) & b)
  if ~isempty(intersect(Qt,M.F))
    % we've reached a final state
    b = 0;
  else
    Qt1 = [];
    for q=Qt
      for s=double(M.ALF)
	r = dfsa_delta(M,q,s);
	Qt1(end+1) = r;
      end
    end
    Qt = unique(Qt1);
    t = t + 1;
  end
end

return