Abstract
Davenport and Erdős [3] proved that every setA of integers with the property thata ∈A impliesan ∈A for alln (multiplicative ideal) has a logarithmic density. I generalized [5] this result to sets with the property that if for some numbersa, b, n we havea ∈ A, b ∈ A andan ∈ A, then necessarilybn ∈ A, which I call quasi-ideals.
Here a new proof of this theorem is given, applying a result on convolution of measures on discretes semigroups. This leads to further generalizations, including an improvement of a result of Warlimont [8] on ideals in abstract arithmetic semigroups.
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Supported by Hungarian National Foundation for Scientific Research, Grant No. 1901
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Ruzsa, I.Z. Logarithmic density and measures on semigroups. Manuscripta Math 89, 307–317 (1996). https://doi.org/10.1007/BF02567519
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DOI: https://doi.org/10.1007/BF02567519