An Elementary Characterization of the Category of (Free) Relational Systems.
An elementary proof that finite groups are projectively torsion-free
Applications logiques en théorie des anneaux et des modules
Automorphisms of categories of free algebras of varieties.
Bijective reflexions and coreflexions of commutative unars
Cartesian closedness in categories of partial algebras.
Categorical equivalences of varieties generated by algebras and
Categories of functors between categories with partial morphisms
It is well-known that the composition of two functors between categories yields a functor again, whenever it exists. The same is true for functors which preserve in a certain sense the structure of symmetric monoidal categories. Considering small symmetric monoidal categories with an additional structure as objects and the structure preserving functors between them as morphisms one obtains different kinds of functor categories, which are even dt-symmetric categories.
Categories of locally diagonal partial algebras.
Central extensions in Mal'tsev varieties.
Centrality and normality in protomodular categories.
Characterization of protomodular varieties of universal algebras.
Classes of graphs definable by graph algebra identities or quasi-identities
Clone properties of topological spaces
Clone properties are the properties expressible by the first order sentence of the clone language. The present paper is a contribution to the field of problems asking when distinct sentences of the language determine distinct topological properties. We fully clarify the relations among the rigidity, the fix-point property, the image-determining property and the coconnectedness.
Clones in topology and algebra.
Closedness properties of internal relations. IV: Expressing additivity of a category via subtractivity.
Colimits of representable algebra-valued functors.
Completely dissociative groupoids
In a groupoid, consider arbitrarily parenthesized expressions on the variables where each appears once and all variables appear in order of their indices. We call these expressions -ary formal products, and denote the set containing all of them by . If are distinct, the statement that and are equal for all values of is a generalized associative law. Among other results, we show that many small groupoids are completely dissociative, meaning that no generalized associative law holds...
Complétion et complétude selon H. Andreka et I. Nemeti
Congruence relations on finitary models