In arithmetic, a twofold connection on a set An is an accumulation of requested matches of components of A. In different expressions, its a subset of the Cartesian feature A2 = A × A. Ordinarily, a binary connection between two sets An and B is a subset of A × B. The terms dyadic connection and 2-place connection are synonyms for double relations.

An illustration is the “partitions” connection between the set of prime numbers P and the set of numbers Z, in which each prime p is connected with each number z that is a various of p (and not with any whole number that is not a different of p). In this connection, for example, the prime 2 is connected with numbers that incorporate −4, 0, 6, 10, anyway not 1 or 9; and the prime 3 is connected with numbers that incorporate 0, 6, and 9, be that as it may not 4 or 13.