function M3 = concat_nfsa(M1,M2)
% M3 is the nfsa-concatenation of M1 and M2
% see str2nfsa.m for basic dfsa definitions

M3 = M1;

nQ1 = length(M1.Q);
nQ2 = length(M2.Q);
%nQ3 = nQ1 + nQ2 + 1;  % wasteful
nQ3 = nQ1 + nQ2;
M3.Q = 1:nQ3;

q_link = nQ1 + M2.q0; % the linking state

M3.F = M2.F + nQ1;

% make all the accept states of M1 point to q_link
for q=M1.F
  R = nfsa_delta(M1,q,'@');
  M3 = set_ndelta(M3,[q],['@'],{union(R,q_link)});
end

%treat all states of M2 as incremented by nQ1

for q = M2.Q
  for s = M2.ALF
    R = nfsa_delta(M2,q,s);
    %M3 = set_ndelta(M3,[q+q_link],[s],{R+q_link});
    %M3 = set_ndelta(M3,[q+q_link-1],[s],{R+q_link-1}); %no longer a new state
    M3 = set_ndelta(M3,[q+nQ1],[s],{R+nQ1}); %no longer a new state
  end
end
    
return