Functorial algebras and automata
Functorial uniform reducibility
Galois theory and double central extensions.
General algebraic geometry and formal concept analysis.
Generalization of the concept of variety and quasivariety to partial algebras through category theory [Book]
Generalized deductive systems in subregular varieties
An algebra is subregular alias regular with respect to a unary term function if for each we have whenever for each . We borrow the concept of a deductive system from logic to modify it for subregular algebras. Using it we show that a subset is a class of some congruence on containing if and only if is this generalized deductive system. This method is efficient (needs a finite number of steps).
Generalized varieties of commutative and nilpotent semigroups.
Generalizing substitution
It is well known that, given an endofunctor on a category , the initial -algebras (if existing), i.e., the algebras of (wellfounded) -terms over different variable supplies , give rise to a monad with substitution as the extension operation (the free monad induced by the functor ). Moss [17] and Aczel, Adámek, Milius and Velebil [2] have shown that a similar monad, which even enjoys the additional special property of having iterations for all guarded substitution rules (complete iterativeness),...
Generalizing Substitution
It is well known that, given an endofunctor H on a category C , the initial (A+H-)-algebras (if existing), i.e. , the algebras of (wellfounded) H-terms over different variable supplies A, give rise to a monad with substitution as the extension operation (the free monad induced by the functor H). Moss [17] and Aczel, Adámek, Milius and Velebil [12] have shown that a similar monad, which even enjoys the additional special property of having iterations for all guarded substitution rules (complete...
Generators of free universal algebras.
Group conjugation has non-trivial LD-identities
We show that group conjugation generates a proper subvariety of left distributive idempotent groupoids. This subvariety coincides with the variety generated by all cancellative left distributive groupoids.
Hereditary properties of algebras with respect to inductive limits
Homomorphic images of finite subdirectly irreducible unary algebras
We prove that a finite unary algebra with at least two operation symbols is a homomorphic image of a (finite) subdirectly irreducible algebra if and only if the intersection of all its subalgebras which have at least two elements is nonempty.
How algebraic is algebra?
How much semigroup structure is needed to encode graphs ?
Hu's Primal Algebra Theorem revisited
It is shown how Lawvere's one-to-one translation between Birkhoff's description of varieties and the categorical one (see [6]) turns Hu's theorem on varieties generated by a primal algebra (see [4], [5]) into a simple reformulation of the classical representation theorem of finite Boolean algebras as powerset algebras.
Hyperassociative varieties of semigroups.
Hyperidentities and hypervarieties.
Hyperidentities in associative graph algebras
Graph algebras establish a connection between directed graphs without multiple edges and special universal algebras of type (2,0). We say that a graph G satisfies an identity s ≈ t if the correspondinggraph algebra A(G) satisfies s ≈ t. A graph G is called associative if the corresponding graph algebra A(G) satisfies the equation (xy)z ≈ x(yz). An identity s ≈ t of terms s and t of any type τ is called a hyperidentity of an algebra A̲ if whenever the operation symbols occurring in s and t are replaced...
Hyperidentities in many-sorted algebras
The theory of hyperidentities generalizes the equational theory of universal algebras and is applicable in several fields of science, especially in computers sciences (see e.g. [2,1]). The main tool to study hyperidentities is the concept of a hypersubstitution. Hypersubstitutions of many-sorted algebras were studied in [3]. On the basis of hypersubstitutions one defines a pair of closure operators which turns out to be a conjugate pair. The theory of conjugate pairs of additive closure operators...