The mathematician Hugo Ribeiro.
Residually finite congruences and quasi-regular subsets in uniform algebras
An elementary proof that finite groups are projectively torsion-free
On the power semigroup of a finite semigroup
On regular implicit operations
Some pseudovariety joins involving the pseudovariety of finite groups.
The globals of pseudovarieties of ordered semigroups containing and an application to a problem proposed by Pin
Given a basis of pseudoidentities for a pseudovariety of ordered semigroups containing the 5-element aperiodic Brandt semigroup , under the natural order, it is shown that the same basis, over the most general graph over which it can be read, defines the global. This is used to show that the global of the pseudovariety of level of Straubing-Thérien’s concatenation hierarchy has infinite vertex rank.
The globals of pseudovarieties of ordered semigroups containing and an application to a problem proposed by Pin
Given a basis of pseudoidentities for a pseudovariety of ordered semigroups containing the 5-element aperiodic Brandt semigroup , under the natural order, it is shown that the same basis, over the most general graph over which it can be read, defines the global. This is used to show that the global of the pseudovariety of level of Straubing-Thérien's concatenation hierarchy has infinite vertex rank.
The pseudovariety of semigroups of triangular matrices over a finite field
We show that semigroups representable by triangular matrices over a fixed finite field form a decidable pseudovariety and provide a finite pseudoidentity basis for it.
The pseudovariety of semigroups of triangular matrices over a finite field
We show that semigroups representable by triangular matrices over a fixed finite field form a decidable pseudovariety and provide a finite pseudoidentity basis for it.
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