Sentence examples for problem is difficult from inspiring English sources

The problem is difficult enough already.

"You don't walk away when the problem is difficult".

The problem is difficult to contain, experts say.

The problem is difficult to study for a number of reasons.

Even with the best of will, this problem is difficult to crack.

Even though the problem is difficult, once you see optimal route it seems so obvious!

A problem is difficult if an appropriate sequence of steps to solve it is not known.

In spite of its simple and natural formulation, this problem is difficult to solve.

The underlying mathematical problem is difficult to solve because it involves infinite stability and controllability constraints.

Optimal solution of the advanced tolerance design problem is difficult with the traditional optimization techniques.

The problem is difficult and has been approached by numerous research groups in the past.