Start
  f_0
    e_1
      '1'@(1:1-1:2)
      e_2
        '1'@(1:2-1:3)
        e_0
          '0'@(1:3-1:4)
        x
          '2'@(1:4-1:5)
  Eof@(1:5-1:5)=''