11.   He begins to befriend the older scientist and is able to convince Scalapino to work with him on a theoretical problem.

12.   The debate, once a theoretical problem, has in the computer age become a practical one.

13.   The prospect of applying the rational-basis test in the case Monday posed several theoretical problems for the court.

14.   Then again, it may simply be a theoretical problem.

15.   He added that there would be no theoretical problem in recognizing photocopy rights in a revised copyright law, but that enforcement could prove to be a major headache.