1 INDEX
  Syntax: INDEX [id1][:id2] [&idb][:idb2]

  Alias for `DIRECTORY'.
  Gives an index of the histograms currently in memory. If you specify the
  primary  identifier, you will get  an index of all  histograms with that
  identifier.  To  get all  the  histograms  with a  particular  secondary
  identifier, give the  command `INDEX 0 &idb'.  To get all the histograms
  in a particular range, give the command `INDEX id1:id2 &idb1:idb2'.

