The problem "given two numbers x and y, does x evenly divide y?" is a decision problem.

Combinatorics was introduced by Ramsey to solve a special case of the decision problem for the first-order predicate calculus.

The combinatorics was introduced by Ramsey to solve a special case of the decision problem for the first-order predicate calculus.

The corresponding decision problem consists of deciding whether or not any such homomorphisms exist.