6 6 60 9   Keep diagrams 
 This option can be used to keep diagrams with virtual
particles named by the user. Examples:
1) Z>2 (keeps diagrams with more than 2 virtual Z-boson.)
2) Z<2 (keeps diagrams with less than 2 virtual Z-boson.)
3) Z=2 (keeps diagrams with 2 virtual Z-boson.)
4) Z!2 (excludes diagrams with only 2 virtual Z-boson.)
5) Z   (keeps all diagrams with at least 1 Z-boson.)

  Use empty input to get the full set of diagrams.

Warning! This option works with the diagram set obtained
         after of applying of exclude conditions.