Zobrazeno 1 - 10
of 123
pro vyhledávání: '"Valdis Laan"'
Autor:
Valdis Laan, Marilyn Kutti
Publikováno v:
Categories and General Algebraic Structures with Applications, Vol 21, Iss 1, Pp 1-17 (2024)
In this paper we study multiplicative semigroups of $2\times 2$ matrices over a linearly ordered abelian group with an externally added bottom element. The multiplication of such a semigroup is defined by replacing addition and multiplication by join
Externí odkaz:
https://doaj.org/article/68b6e09e69c74321aa462133624ca4a6
Publikováno v:
Categories and General Algebraic Structures with Applications, Vol 15, Iss 1, Pp 59-92 (2021)
In this paper we study flatness properties (pullback flatness, limit flatness, finite limit flatness) of acts over semigroups. These are defined by requiring preservation of certain limits from the functor of tensor multiplication by a given act. We
Externí odkaz:
https://doaj.org/article/5f8a87da71334e2a867fd582f89c7136
Autor:
Kristo Väljako, Valdis Laan
Publikováno v:
Proceedings of the Estonian Academy of Sciences, Vol 70, Iss 2, Pp 122-134 (2021)
In this paper we study Morita contexts between rings without identity. We prove that if two associative rings are connected by a Morita context with surjective mappings, then these rings have isomorphic quantales of unitary ideals. We also show that
Externí odkaz:
https://doaj.org/article/aa44a6d859f04c00a76b53c983daa5a9
Autor:
Valdis Laan, Alvin Lepik
Publikováno v:
Proceedings of the Edinburgh Mathematical Society. :1-29
We call a semigroup right perfect if every object in the category of unitary right acts over that semigroup has a projective cover. In this paper, we generalize results about right perfect monoids to the case of semigroups. In our main theorem, we wi
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::fd7cf56afb35b3b74f1a68852f9becf3
https://doi.org/10.1017/s0013091523000159
https://doi.org/10.1017/s0013091523000159
Publikováno v:
Semigroup Forum. 102:842-860
Two semigroups are called Morita equivalent if the categories of firm right acts over them are equivalent. We prove that every semigroup is Morita equivalent to its subsemigroup consisting of all products of n factors. Using this we show that a finit
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::2149f682498a2c58203675cf5f078ed4
https://doi.org/10.1007/s00233-020-10153-y
https://doi.org/10.1007/s00233-020-10153-y
Autor:
Kristo Väljako, Valdis Laan
Publikováno v:
Communications in Algebra. 49:1764-1772
We introduce enlargements of rings as additive analogues of enlargements of semigroups. For example, a full matrix ring over an idempotent ring is an enlargement of that ring. As our main result we...
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::3728929e5f6a5711202179ff198c2f90
https://doi.org/10.1080/00927872.2020.1851702
https://doi.org/10.1080/00927872.2020.1851702
Publikováno v:
Algebra universalis. 82
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::8e1565f9dc5cb01cf08e705f43c809cb
https://doi.org/10.1007/s00012-021-00749-y
https://doi.org/10.1007/s00012-021-00749-y
Autor:
Ülo Reimaa, Valdis Laan
Publikováno v:
Studia Scientiarum Mathematicarum Hungarica. 56:267-279
We prove that in the category of firm acts over a firm semigroup monomorphisms co-incide with regular monomorphisms and we give an example of a non-injective monomorphism in this category. We also study conditions under which monomorphisms are inject
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::aacd2e31cb753a6ff98032c2dbf17dee
https://doi.org/10.1556/012.2019.56.3.1432
https://doi.org/10.1556/012.2019.56.3.1432
Autor:
Valdis Laan, Ülo Reimaa
Publikováno v:
International Journal of Algebra and Computation. 29:723-741
A semigroup is called factorizable if each of its elements can be written as a product. We study equivalences and adjunctions between various categories of acts over a fixed factorizable semigroup. We prove that two factorizable semigroups are Morita
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::9987a6b4869a01bd558af1d73c24dd2a
https://doi.org/10.1142/s0218196719500243
https://doi.org/10.1142/s0218196719500243
Publikováno v:
Algebra universalis. 81
We study properties of the lattice of unitary ideals of a semigroup. In particular, we show that it is a quantale. We prove that if two semigroups are connected by an acceptable Morita context then there is an isomorphism between the quantales of uni
Externí odkaz:
https://explore.openaire.eu/search/publication?articleId=doi_________::18993850ebf264886c17d7e88b992806
https://doi.org/10.1007/s00012-020-0650-0
https://doi.org/10.1007/s00012-020-0650-0