Perhaps you should try some spelling variations:
communication problem » communication problems, communications problems, communication program
restriction recursion » extraction recursion, restriction production, restriction design
communication root » communication robot, communication room, communication robots
recursion level » decision level, recursion removal

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: communication ((communication root) OR (communication problem)) restriction recursion level~.
• Adding a wildcard symbol may retrieve word variants: communication ((communication root) or (communication problem)) restriction recursion level*.