function M = custnfsa(L)
M.Q = 1:L+1;
M.F = [1, L+1];
M.ALF = '@ab';
M.q0 = 1;

M = set_ndelta(M,[1]  ,'a',{[2:L+1]});
M = set_ndelta(M,[L+1],'b',{[1:L  ]});

M = set_ndelta(M,[1],'b',{[2]});
M = set_ndelta(M,[L+1],'a',{[L]});

for j=2:L
  M = set_ndelta(M,[j],'a',{[j-1]});
  M = set_ndelta(M,[j],'b',{[j+1]});
end  

return
M = str2nfsa('aaa','ab');
M.F = [1 4];
M = set_ndelta(M,[1],'a',{[2 3 4]});
M = set_ndelta(M,[4],'b',{[1 2 3]});

M = set_ndelta(M,[1],'b',{[2]});

M = set_ndelta(M,[4],'a',{[3]});

M = set_ndelta(M,[2],'a',{[1]});
M = set_ndelta(M,[2],'b',{[3]});

M = set_ndelta(M,[3],'a',{[2]});
M = set_ndelta(M,[3],'b',{[4]});


return