       a       0      x0 # a.0        a       0      x0 # a.0        a       0      x0 # a.0        a       0      x0 # b.00       b       0      x0 # b.00       b       0      x0 # b.00       b       0      x0 # b.00       b       0      x0 # b.00       b       0      x0