On some systems of equations with constraints in a free group. – Addenda. (Sur certains systèmes d'équations avec constraintes dans un groupe libre. – Addenda.)
On some systems of equations with constraints in a free group. (Sur certains systèmes d'équations avec contraintes dans un groupe libre.)
Some algorithms on the star operation applied to finite languages.
Some quasi-ordered classes of finite commutative semigroups.
Semidirectly closed pseudovarieties of locally trivial semigroups.
Power pseudovarieties of semigroups I.
On the membership problem for pseudo-varieties of commutative semigroups.
Power pseudovarieties of semigroups II.
A unified syntactical approach to theorems of Putcha, Margolis, and Straubing on finite power semigroups.
Sign changes of error terms related to arithmetical functions
Let . Motivated by a conjecture of Erdös, Lau developed a new method and proved that We consider arithmetical functions whose summation can be expressed as , where is a polynomial, and . We generalize Lau’s method and prove results about the number of sign changes for these error terms.
Generalized varieties of commutative and nilpotent semigroups.
The pseudovariety is hyperdecidable
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