Perhaps you should try some spelling variations:
cooperation systems » cooperation system, cooperative systems, cooperating systems
operation systems » operations systems, operation system, operational systems
operations system » operations systems, operation system, operational system

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((( operation systems ) OR ( cooperation systems ))) OR ( operations system )).
• Adding a wildcard symbol may retrieve word variants: (((( operation systems ) or ( cooperation systems ))) or ( operations system ))*.