A kind of puzzle in which there is one common factor in a first set of diagrams that is missing from a second set. The solver (possibly a computer program) must identify this factor.

To solve problems.

(mathematics) The question as to the value of ∑ₙ₌₁ ᪲1/(n²), the sum of the reciprocals of the squares of the positive integers.

(euphemistic) A child who is particularly difficult to raise or educate, especially due to a lack of self-control and disruptive and antisocial behavior.

A mental representation of a particular problem, including initial, final and possible intermediate states

An observation that contradicts an accepted law or theory.

(computer science) The problem of deciding in finite time whether a given program will finish running in finite time, when given a certain finite input.

(probability theory) The mathematics problem that concerns the probability there exist two people in a random group who share a birthday.

(programming) A problem dealing with how to treat the initial or boundary values of a discrete problem.

A problem that has been posed in a field of study such as mathematics or theoretical computer science, but whose answer is not yet known.