11.   At first, many were skeptical that boosting was anything more than a theoretical concept.

12.   But as a theoretical concept it might explain some of the properties of real glass.

13.   Homeland security, the task of the new Cabinet-level post created by President Bush this week, is no theoretical concept here.

14.   It is easy to approve a theoretical concept but quite another thing to vote for a specific figure with a specific agenda.

15.   Several instructors said beginner-level software is an excellent reinforcement for theoretical concepts, and that young students seem to retain them better.

16.   The observations fit the classic definition of a black hole, a theoretical concept until the Hubble observations.

17.   Those are theoretical concepts.