A Jónsson-Tarski algebra is a set together with an isomorphism .
Clearly (at least in classical mathematics), any Jónsson-Tarski algebra is either empty, a singleton, or infinite.
The structure of a Jónsson-Tarski algebra can be described by an algebraic theory, with one binary operation and two unary operations and such that , , and .
The category of Jónsson-Tarski algebras is a topos, although this is not in general the case for algebraic theories. See here.
Revised on March 2, 2014 15:43:53
by Tim Campion?