Perhaps you should try some spelling variations:
"cooperation systems" » "cooperation system", "cooperative systems", "cooperating systems"
"operational systems" » "operating systems", "operation system", "conversational systems"
"relational systems" » "national systems", "educational systems", "functional systems"

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: (("cooperation systems") OR ((("operational systems") OR ("relational systems")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"cooperation systems\") or (((\"operational systems\") OR (\"relational systems\"))))".
• Removing quotes may allow a broader search: (( cooperation systems ) or ((( operational systems ) OR ( relational systems )))).
• Adding a wildcard symbol may retrieve word variants: (("cooperation systems") or ((("operational systems") OR ("relational systems"))))*.