Sheaf constructions in universal algebra and model theory
Simplicity of algebras requires to investigate almost all operations
Some decidable congruences of free monoids
Let be the free monoid over a finite alphabet . We prove that a congruence of generated by a finite number of pairs , where and , is always decidable.
Some decidable theories with finitely many covers which are decidable and algorithmically found
In any recursive algebraic language, I find an interval of the lattice of equational theories, every element of which has finitely many covers. With every finite set of equations of this language, an equational theory of this interval is associated, which is decidable with decidable covers that can be algorithmically found. If the language is finite, both this theory and its covers are finitely based. Also, for every finite language and for every natural number n, I construct a finitely based decidable...
Some embedding theorems.
Special m-hyperidentities in biregular leftmost graph varieties of type (2,0)
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 a term equation s ≈ t if the corresponding graph algebra satisfies s ≈ t. A class of graph algebras V is called a graph variety if where Σ is a subset of T(X) × T(X). A graph variety is called a biregular leftmost graph variety if Σ’ is a set of biregular leftmost term equations. A term equation s ≈ t is called an identity in a variety...
Structures pseudo-algébriques (1ère partie)