Associator


In abstract algebra, the term associator is used in different ways as a measure of the nonassociativity of an algebraic structure. Associators are commonly studied as triple systems.

Ring theory

For a nonassociative ring or algebra, the associator is the multilinear map given by
Just as the commutator
measures the degree of noncommutativity, the associator measures the degree of nonassociativity of.
For an associative ring or algebra the associator is identically zero.
The associator in any ring obeys the identity
The associator is alternating precisely when is an alternative ring.
The associator is symmetric in its two rightmost arguments when is a pre-Lie algebra.
The nucleus is the set of elements that associate with all others: that is, the n in R such that
The nucleus is an associative subring of R.

Quasigroup theory

A quasigroup Q is a set with a binary operation such that for each a,b in Q,
the equations and have unique solutions x,y in Q. In a quasigroup Q, the
associator is the map defined by the equation
for all a,b,c in Q. As with its ring theory analog, the quasigroup associator is a measure of nonassociativity of Q.

Higher-dimensional algebra

In higher-dimensional algebra, where there may be non-identity morphisms between algebraic expressions, an associator is an isomorphism

Category theory

In category theory, the associator expresses the associative properties of the internal product functor in monoidal categories.