Quasivariety

- Mathematics & Logic -
Pure Mathematics Dictionary
A class of algebras axiomatizable by a set of universal Horn sentences; equivalently, a class closed under taking subalgebras, direct products and ultraproducts (and containing the trivial algebra when required).

Quasivariety

- Pure Mathematics -
Algebra Dictionary
A class of algebras axiomatizable by universal Horn sentences (quasi‑identities); equivalently a class closed under subalgebras, direct products, and ultraproducts (and isomorphisms), but not necessarily under homomorphic images.