Extensions of algebraic systems
Awad A. Iskander · Transactions of the American Mathematical Society · 1984
There are several generalizations to universal algebras of the notion "The group A \mathfrak {A} is an extension of the group B \mathfrak {B} by the group C \mathfrak {C} ". In this paper we study three such generalizations and the corresponding products of classes of algebraic systems. Various results are presented. One such theorem characterizes the weakly congruence regular varieties admitting extensions of a particular sort. Another result gives, under a weak congruence permutability condition, an equational basis for the variety obtained by applying one such product to two other varieties.