Perhaps you should try some spelling variations:
cooperation systems » cooperation system, cooperative systems, cooperating systems
operations systems » operations system, operational systems, operating systems
operation system » operating system, operating systems, generation 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 system ) OR ( cooperation systems ))) OR ( operations systems )).
• Adding a wildcard symbol may retrieve word variants: (((( operation system ) or ( cooperation systems ))) or ( operations systems ))*.