\begin{theindex}

  \item_0 a(0) 1
    \item_01 a(1) 2
      \item_12 a(2) 3
        \item_23 a(3) 4
          \item_34 a(4) 5
  \item_0 ab(0) 6
  \item_0 ac
    \item_x1 a
      \item_x2 a
        \item_x3 a
          \item_x4 a(4) 7
  \item_0 ad
    \item_x1 a(1) 8
    \item_1 b(1) 9
      \item_12 a
        \item_x3 a
          \item_x4 a(4) 10
  \item_0 ae
    \item_x1 a
      \item_x2 a(2) 11
    \item_1 b
      \item_x2 b(2) 12
        \item_23 a
          \item_x4 a(4) 13
  \item_0 af
    \item_x1 b
      \item_x2 a
        \item_x3 a(3) 14
      \item_2 b
        \item_x3 b(3) 15
          \item_34 a(4) 16
  \item_0 ag
    \item_x1 b
      \item_x2 b
        \item_x3 a(3) 17
        \item_3 b(3) 18
          \item_34 a(4) 19

  \indexspace

  \item_0 pa(0) 21
    \item_01 qa
      \item_x2 ra(2) 22
  \item_0 pb(0) 23
    \item_01 qb
      \item_x2 rb
        \item_x3 sb(3) 24
  \item_0 pc(0) 25
    \item_01 qc
      \item_x2 rc
        \item_x3 sc
          \item_x4 tc(4) 26
  \item_0 pd
    \item_x1 qd(1) 27
      \item_12 rd
        \item_x3 sd(3) 28
  \item_0 pe
    \item_x1 qe(1) 29
      \item_12 re
        \item_x3 se
          \item_x4 te(4) 30
  \item_0 pf
    \item_x1 qf
      \item_x2 rf(2) 31
        \item_23 sf
          \item_x4 tf(4) 32

  \indexspace

  \item_0 xa(0) 1
  \item_0 xb(0) 1
  \item_0 xc(0) 1

  \indexspace

  \item_0 ya
    \item_x1 x(1) 1
    \item_1 y(1) 1
    \item_1 z(1) 1
  \item_0 yb
    \item_x1 x
      \item_x2 x(2) 1
      \item_2 y(2) 1
      \item_2 z(2) 1
  \item_0 yc
    \item_x1 x
      \item_x2 y
        \item_x3 x(3) 1
        \item_3 y(3) 1
        \item_3 z(3) 1
  \item_0 yd
    \item_x1 x
      \item_x2 y
        \item_x3 z
          \item_x4 x(4) 1
          \item_4 y(4) 1
          \item_4 z(4) 1

\end{theindex}