1 SUBTRACT
  Syntax: SUBTRACT id1[:id1n] [&idb1] id2[:id2n] [&idb2] id3[:id3n] [&idb3]
          scale1 scale2                           (default scale = 1.0 1.0)
   where: id1,id2   are the input histogram identifiers
          id3       is the output histogram identifier
          idb1,idb2 are the (optional) input secondary identifiers
     and  idb3      is the (optional) output secondary identifier

  Subtracts two  histograms (`id1,  id2') to make a  third one. To specify
  the secondary  identifier,  precede it by  a `&',  otherwise the default
  will be used.  (Use the  `SET IDB' command  to change  the default). The
  scale factors are optional. To avoid confusion, you should give a `<CR>'
  after the identifiers  or make sure the scale  factors are given as real
  numbers.

  To subtract a range of histograms,  the primary identifiers you give for
  the input and  output histograms  must be the same,  but you can specify
  different   secondary  identifiers.  For  example,
  `SUBTRACT    300:400&1  300:400&2  300 :  400 &  10'  will  subtract all
  histograms with primary identifiers 300 to 400 and secondary identifiers
  1, from those  with  secondary identifiers  2, putting  the results into
  histograms with  the same primary  identifiers and  secondary identifier
  10. If you give primary identifier 0, the operation will be performed on
  all plots with the given secondary identifier.

