On equalizers in generalized algebraic categories Pavel Pták (1972) Commentationes Mathematicae Universitatis Carolinae
On locally small based algebraic theories Jan Reiterman (1986) Commentationes Mathematicae Universitatis Carolinae
On the failure of Birkhoff's theorem for locally small based equational categories of algebras Horst Herrlich (1993) Cahiers de Topologie et Géométrie Différentielle Catégoriques