Jónsson term

In universal algebra, within mathematics, a majority term, sometimes called a Jónsson term, is a term t with exactly three free variables that satisfies the equations t = t = t = x.
For example, for lattices, the term ∨ ∨ is a Jónsson term.

Sequences of Jónsson terms

In general, Jónsson terms, more formally, a sequence of Jónsson terms, is a sequence of ternary terms satisfying certain related identities. Being one of the earliest discovered Maltsev conditions, a variety is congruence distributive if and only if it has a sequence of Jónsson terms.
The case of a majority term is given by the special case n=2 of a sequence of Jónsson terms.
Jónsson terms are named after the Icelandic mathematician Bjarni Jónsson.