But he's dealing with difficult material and doing so in intriguing ways that would seem to allow plenty of room for growth.

It also comes as a respite after some much more difficult material.

As one student said, "The most difficult material is at the beginning - and then it gets harder."

"They convinced me there would in fact be a way of handling this very difficult material."

There is no doubt that current students are much better prepared for difficult material.

But these authors are working with more difficult material.

Its main use is to carry difficult materials at slow speed.

Some of this involves the more difficult material the author presents.

"They tackle difficult material and deal with problems we are facing today."

"Goose down is a very difficult material to measure and qualify," he said.