Geodesic
Weak alg-universality and $Q$-universality of semigroup quasivarieties
Commentationes Mathematicae Universitatis Carolinae, Tome 46 (2005) no. 2, pp. 257-279 Cet article a éte moissonné depuis la source Czech Digital Mathematics Library

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In an earlier paper, the authors showed that standard semigroups $\bold M_1$, $\bold M_2$ and $\bold M_3$ play an important role in the classification of weaker versions of alg-universality of semigroup varieties. This paper shows that quasivarieties generated by $\bold M_2$ and $\bold M_3$ are neither relatively alg-universal nor $Q$-universal, while there do exist finite semigroups $\bold S_2$ and $\bold S_3$ generating the same semigroup variety as $\bold M_2$ and $\bold M_3$ respectively and the quasivarieties generated by $\bold S_2$ and/or $\bold S_3$ are quasivar-relatively $f\!f$-alg-universal and $Q$-universal (meaning that their respective lattices of subquasivarieties are quite rich). An analogous result on $Q$-universality of the variety generated by $\bold M_2$ was obtained by M.V. Sapir; the size of our semigroup is substantially smaller than that of Sapir's semigroup.
In an earlier paper, the authors showed that standard semigroups $\bold M_1$, $\bold M_2$ and $\bold M_3$ play an important role in the classification of weaker versions of alg-universality of semigroup varieties. This paper shows that quasivarieties generated by $\bold M_2$ and $\bold M_3$ are neither relatively alg-universal nor $Q$-universal, while there do exist finite semigroups $\bold S_2$ and $\bold S_3$ generating the same semigroup variety as $\bold M_2$ and $\bold M_3$ respectively and the quasivarieties generated by $\bold S_2$ and/or $\bold S_3$ are quasivar-relatively $f\!f$-alg-universal and $Q$-universal (meaning that their respective lattices of subquasivarieties are quite rich). An analogous result on $Q$-universality of the variety generated by $\bold M_2$ was obtained by M.V. Sapir; the size of our semigroup is substantially smaller than that of Sapir's semigroup.
Classification : 08C15, 18B15, 20M07, 20M99
Keywords: semigroup quasivariety; full embedding; $f\!f$-alg-universality; $Q$-universality 
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     title = {Weak alg-universality and $Q$-universality of semigroup quasivarieties},
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Demlová, M.; Koubek, V. Weak alg-universality and $Q$-universality of semigroup quasivarieties. Commentationes Mathematicae Universitatis Carolinae, Tome 46 (2005) no. 2, pp. 257-279. http://geodesic.mathdoc.fr/item/CMUC_2005_46_2_a3/