Lesokhin, M. M.; Popyrin, A. V.; Ermolina, N. G. Bicharacters of semigroups. (Russian) Zbl 0736.20041 Homomorphisms, Interuniv. Collect. Sci. Works, Leningrad, 60-70 (1988). MSC: 20M15 20M20 20M30 PDFBibTeX XMLCite \textit{M. M. Lesokhin} et al., in: Duality of commutative semigroups. . 60--70 (1988; Zbl 0736.20041)
Ermolina, N. G. On approximation of commutative semigroups by real and finite bicharacters. (Russian) Zbl 0743.20063 Homomorphisms, Interuniv. Collect. Sci. Works, Leningrad, 27-43 (1988). MSC: 20M14 20M30 PDFBibTeX XMLCite \textit{N. G. Ermolina}, in: Duality of commutative semigroups. . 27--43 (1988; Zbl 0743.20063)