0.  u=[   ]  w = 1
  0.  u=[ ba]  w = -10
  0.  u=[aca]  w = -10
  0.  u=[ aa]  w = -10

  0.  u=[ ca]  w = -10


  0.  u=[  b]  w = -1
  0.  u=[ cb]  w = 1

  0.  u=[ ab]  w = 1