The phrase "a set of difficult" is not complete and requires additional context to be correct and usable in written English.
It can be used when referring to a collection of challenging tasks, problems, or situations, but it needs to be followed by a noun to clarify what is difficult.
Example: "The teacher assigned a set of difficult problems for the students to solve."
Alternatives: "a collection of challenging" or "a group of tough".
In a paper for the journal Memory, psychologists Benjamin Storm, Sean Stone, and Aaron Benjamin describe how they first asked people a set of difficult trivia questions.
To my parents and their friends, the Yugoslav motel was an unquestioned paradise, a lucky coda to a set of difficult lives.
"Just like that last helicopter on the embassy roof in Vietnam, we witnessed a set of difficult images last night that will be forever engraved in our collective consciousness," Hemi Shalev said in the newspaper Maariv today.
To complain that "The Passion of the Christ" is possessed by death makes no sense, because Christianity itself makes no sense without the shroud of death; the story of Jesus, shorn of its climactic sufferings, dwindles into a set of difficult ethics.
Generally, a set of difficult nonlinear algebraic equations appear when harmonic balance method is imposed.
It is validated over a set of difficult test problems with exact solution and its multi-dimensional capabilities are shown over problems involving a large number of materials.
Rivals can hardly match an array of interlocked activities if firms have a set of difficult-to-imitate implementations.
When a student finds a topic too easy, one may get a set of more difficult questions to solve; but in the case of finding it too difficult, one may obtain some supplementary learning materials to clear the obstacles.
The performance for a group of 15 symptomatic readers was examined as compared with 15 screening personnel over a set of 60 difficult mammographic cases that contained a range of features and mammographic classification types.
But this shift to a Networked Economy raises a new set of difficult questions that will take decades to even begin to answer.
Each year the majority of these film-readers interpret a 'PERFORMS' set of difficult cases as a means of self-assessing their skills.
