function M=prune_eps(M)
% a technical routine to disconnect unnecessary states

for q=M.Q
  E = just_eps(q,M);
  if (length(E)==1) %there is exactly one exclusive epsilon-child
    M = replace(q,E(1),M);
  end
end
return

function set1 = setrepl(set1,p,q)
%replace all occurrences of p w/q in set1
if ~isempty(set1)
  set1(find(set1==p)) = q;
end
return

function M = replace(q1,p1,M)
% make everything that pointed to q now point to p
M.q0 = setrepl(M.q0,q1,p1);
M.F  = setrepl(M.F ,q1,p1);
for q = M.Q
  for s = M.ALF
    R = nfsa_delta(M,q,s);
    R = setrepl(R,q1,p1);
    M = set_ndelta(M,[q],[s],{R});
  end
end
return

function E = just_eps(q,M)
% if the only transitions out of q are epsilon-transitions
% E is a list of q's children
% otherwise, E is empty

E = nfsa_delta(M,q,'@');
if (length(E)==1)
  % it's a candidate
  for s=M.ALF(2:end)
    R = nfsa_delta(M,q,s);
    if ~isempty(R)
      % other children -- abort
      E = [];
      break;
    end
  end
end