1.   In a similar way it is possible to phrase many other unsolved mathematical problems in terms of the Turing machine halting problem.

2.   But for every reported success, there are, unfortunately, too many failures and unsolved problems.

3.   But others caution that there are still unsolved problems with using nanotubes as microscope tips.

4.   Ford resisted entreaties from Gowell and other colleagues to deal with his unsolved emotional problems, she said.

5.   If they try to solve an unsolved problem, and fail, they have no way of knowing whether they missed something obvious.

6.   Riemann is another outstanding unsolved problem.

7.   Russian scientists are no less aware of the unsolved problems of missile defense than their American counterparts.

8.   The display examines the unsolved problem of supply vs. demand.

9.   The goal is to focus the public and political leaders on the unsolved problem of hunger.

10.   What to do with the old mausoleum, now graffiti-covered and neglected, is an unsolved problem.