Historical data is a difficult set of data to work with due to multiple factors.

Nicklaus calls the greens here the "the most difficult set in the world."

For the technical crew members, the film's human characters posed a difficult set of challenges.

The second reason for this meeting, the commander said, is the difficult set of circumstances in which we find ourselves.

None of the problems from qualifying were repeated, as she went through her difficult sets without major errors.

It is a difficult set of numbers to parse.

We have a highly difficult set of issues to deal with here.

These are the most difficult set of greens in the world that I know of.

"It's a very difficult set of issues, but I think that people will work at it," Vincent said.

During my time here they gave me full support through what was often a difficult set of circumstances.