He thinks that war is a necessary evil.

Do you understand the necessity of this project?

That information is unnecessary.

That information is completely unnecessary.

Discrete mathematics is an important field that forms the basis of computer science.

He is majoring in applied mathematics at university.

He is passionate about researching pure mathematics.

He is a world-famous mathematician.

Combinatorics is a branch of mathematics that studies combinations of things.

Combinatorics is a branch of mathematics dealing with issues of order and choice.