At last he looked up with the air of a man who had solved a difficult puzzle, but did not like the solution.

Art Llandman had always looked as if he were trying to sort out some difficult puzzle.

That simple fact presented the detective with a more difficult puzzle than he had first assumed.

It's been a difficult puzzle to put together, but that's why I don't move too quickly.

She had been trained her entire life to be able to solve the most difficult military puzzles.

He stated that it was both dramatic and exciting, but also a difficult puzzle.

It wasn't a difficult puzzle, which didn't make the solution easier to live with.

In a second test, subjects had to solve a difficult puzzle using the same pegs and board.

Some more difficult puzzles may also require several types of "what if?"

It was like having a huge, amazingly difficult puzzle to do, really.