For each regular language L we describe a family of canonical nondeterministic acceptors (nfas). Their construction follows a uniform recipe: build the minimal dfa for L in a locally finite variety V , and apply an equivalence between the finite V-algebras and a category of finite structured sets and relations. By instantiating this to different varieties we recover three well-studied canonical...

In categorical universal algebra, it is well known that a finitary equational presentation of algebras in a finitary variety K amounts to the existence of a coequaliser of a pair of morphisms between finitely generated free algebras. The essence of a universal-algebraic flavour of a finitary functor L : K −→ K is that L is determined by its behaviour on finitely generated free algebras. In fact...

For each regular language L we describe a family of canonical nondeterministic acceptors (nfas). Their construction follows a uniform recipe: build the minimal dfa for L in a locally finite variety V, and apply an equivalence between the category of finite V-algebras and a suitable category of finite structured sets and relations. By instantiating this to different varieties, we recover three w...

We show that entropic varieties provide the canonical setting for a generaliziation of Hopf algebra theory. In particular we show that all naturally occurring functors in this context have the expected adjoints, when generalized to this level. In particular, universal measuring comonoids exist over every entropic variety, as do generalized group algebras, and these carry a canonical Hopf struct...

We consider a generalization of the quiver varieties of Lusztig and Nakajima to the case of all symmetrizable Kac-Moody Lie algebras. To deal with the non-simply laced case one considers admissible automorphisms of a quiver and the irreducible components of the quiver varieties fixed by this automorphism. We define a crystal structure on these irreducible components and show that the crystals o...

An extension of parts of the theory of partially ordered varieties and quasivarieties, as presented by Paaasińska and Pigozzi in the framework of abstract algebraic logic, is developed in the more abstract framework of categorical abstract algebraic logic. Algebraic systems, as introduced in previous work by the author, play in this more abstract framework the role that universal algebras play ...

In this paper we investigate the computational complexity of deciding if a given finite algebraic structure satisfies a certain type of existential condition on its set of term operations. These conditions, known as Maltsev conditions, have played a central role in the classification, study, and applications of general algebraic structures. Several well studied properties of equationally define...

Given a directed graph, there exists a universal operator algebra and universal C∗-algebra associated to the directed graph. For finite graphs this algebra decomposes as the universal free product of some building block operator algebras. For countable directed graphs, the universal operator algebras arise as direct limits of operator algebras of finite subgraphs. Finally, a method for computin...

In this paper, we use the theory of natural duality to study subalgebra lattices in the finitely generated varieties of MV-algebras. With this tool, we obtain the dual atomicity of these lattices, and characterize the members of these varieties in which every subalgebra is an intersection of maximal subalgebras. Then, we determine the algebras that have a modular or distributive lattice of suba...