How much semigroup structure is needed to encode graphs ?
Hyperidentities and hypervarieties.
Hyperidentities of groups and semigroups.
Hyperidentities of groups and semigroups. (Short Communication).
Identities of a five-element 0-simple semigroup.
Identities over the two-element alphabet.
Identities valid globally in semigroups.
Infinite words and permutation properties.
Inflation of a union of groups
Inverse monoids and rational Schreier subsets of the free group.
Inverse monoids and rational subsets of related groups.
Isotopy invariant quasigroup identities
According to S. Krstić, there are only four quadratic varieties which are closed under isotopy. We give a simple procedure generating quadratic identities and deciding which of the four varieties they define. There are about 37000 such identities with up to five variables.
Krohn-Rhodes complexity pseudovarieties are not finitely based
We prove that the pseudovariety of monoids of Krohn-Rhodes complexity at most is not finitely based for all . More specifically, for each pair of positive integers , we construct a monoid of complexity , all of whose -generated submonoids have complexity at most .
Krohn-Rhodes complexity pseudovarieties are not finitely based
We prove that the pseudovariety of monoids of Krohn-Rhodes complexity at most n is not finitely based for all n>0. More specifically, for each pair of positive integers n,k, we construct a monoid of complexity n+1, all of whose k-generated submonoids have complexity at most n.
Langages définis par des congruences
Languages recognized by programs over the two-element monoid.
Lattice isomorphisms of commutative relatively free semigroups.
Lattice-theoretically characterized classes of finite bands
There are investigated classes of finite bands such that their subsemigroup lattices satisfy certain lattice-theoretical properties which are related with the cardinalities of the Green’s classes of the considered bands, too. Mainly, there are given disjunctions of equations which define the classes of finite bands.
Le problème de l'associativité des monoïdes et le problème des mots pour les demi-groupes ; algèbres partielles et chaînes élémentaires
Le produit demi-direct pour les demi-groupes inverses.