Nilpotent subsemigroups of a semigroup of order-decreasing transformations of a rooted tree

This paper deals with a semigroup of order-decreasing transformations of a rooted tree.  Such are the transformations \(\alpha\) of some rooted tree \(G\) satisfying following condition: for any \(x\) from \(G\) \(\alpha(x)\) belongs to a simple path from \(x\) to the root vertex of \(G\). We descri...

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Bibliographic Details
Date:2018
Main Author: Stronska, Anna
Format: Article
Language:English
Published: Lugansk National Taras Shevchenko University 2018
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Online Access:https://admjournal.luguniv.edu.ua/index.php/adm/article/view/911
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Journal Title:Algebra and Discrete Mathematics

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Algebra and Discrete Mathematics
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Summary:This paper deals with a semigroup of order-decreasing transformations of a rooted tree.  Such are the transformations \(\alpha\) of some rooted tree \(G\) satisfying following condition: for any \(x\) from \(G\) \(\alpha(x)\) belongs to a simple path from \(x\) to the root vertex of \(G\). We describe all subsemigroups of the mentioned semigroup, which are maximal among nilpotent subsemigroups of nilpotency class \(k\) in our semigroup.  In the event when rooted tree is a ray we prove that all these maximal subsemigroups are pairwise nonisomorphic.