Solvable word problems in semigroups.
Solving word equations
Some (2, n) combinatorial Stein groupoids.
Some (2, n) combinatorial Stein groupoids. (Short Communication).
Some algebraic applications of graded categorical group theory.
Some Algebraic Properties of Machine Poset of Infinite Words
The complexity of infinite words is considered from the point of view of a transformation with a Mealy machine that is the simplest model of a finite automaton transducer. We are mostly interested in algebraic properties of the underlying partially ordered set. Results considered with the existence of supremum, infimum, antichains, chains and density aspects are investigated.
Some algorithms on the star operation applied to finite languages.
Some aspects of Green's relations on periodic semigroups
Some closure properties in monoids.
Some commutativity criteria. - II
Some constructions related to Rees matrix rings.
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 decision problems on integer matrices
Given a finite set of matrices with integer entries, consider the question of determining whether the semigroup they generated 1) is free; 2) contains the identity matrix; 3) contains the null matrix or 4) is a group. Even for matrices of dimension , questions 1) and 3) are undecidable. For dimension , they are still open as far as we know. Here we prove that problems 2) and 4) are decidable by proving more generally that it is recursively decidable whether or not a given non singular matrix belongs...
Some decision problems on integer matrices
Given a finite set of matrices with integer entries, consider the question of determining whether the semigroup they generated 1) is free; 2) contains the identity matrix; 3) contains the null matrix or 4) is a group. Even for matrices of dimension 3, questions 1) and 3) are undecidable. For dimension 2, they are still open as far as we know. Here we prove that problems 2) and 4) are decidable by proving more generally that it is recursively decidable whether or not a given non singular matrix belongs...
Some decompositions of semigroups
Some embedding theorems in varieties of semigroups.
Some finiteness conditions on indecomposable operands.
Some Free Submonoids of the Free Monoid of Prefix Codes.
Some monothetic subsemigroups of S(R).
Some observations on left absolutely flat monoids.