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
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.)
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