We find a sufficient condition for a quasivariety K to have continuum many subquasivarieties that have no independent quasi-equational bases relative to K but have ω-independent quasi-equational bases relative to K. This condition also implies that K is Q-universal.
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A. V. Kravchenko and M. V. Schwidefsky supported by the Grants Council (under RF President) for State Aid of Leading Scientific Schools, grant NSh-6848.2016.1.
M. Nurakunov supported by the International Mathematical Center of Novosibirsk State University.
Translated from Algebra i Logika, Vol. 57, No. 6, pp. 684-710, November-December, 2018.
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Kravchenko, A.V., Nurakunov, A.M. & Schwidefsky, M.V. Structure of Quasivariety Lattices. I. Independent Axiomatizability. Algebra Logic 57, 445–462 (2019). https://doi.org/10.1007/s10469-019-09516-4
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DOI: https://doi.org/10.1007/s10469-019-09516-4