اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe poset of copies for automorphism groups of countable relational structures
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Let $mathrm{G}$ be a subgroup of the symmetric group $mathfrak S(U)$ of all permutations of a countable set $U$. Let $overline{mathrm{G}}$ be the topological closure of $mathrm{G}$ in the function topology on $U^U$. We initiate the study of the poset $overline{mathrm{G}}[U]:={f[U]mid fin overline{mathrm{G}}}$ of images of the functions in $overline{mathrm{G}}$, being ordered under inclusion. This set $overline{mathrm{G}}[U]$ of subsets of the set $U$ will be called the emph{poset of copies for} the group $mathrm{G}$. A denomination being justified by the fact that for every subgroup $mathrm{G}$ of the symmetric group $mathfrak S(U)$ there exists a homogeneous relational structure $R$ on $U$ such that $overline G$ is the set of embeddings of the homogeneous structure $R$ into itself and $overline{mathrm{G}}[U]$ is the set of copies of $R$ in $R$ and that the set of bijections $overline Gcap mathfrak S(U)$ of $U$ to $U$ forms the group of automorphisms of $mathrm{R}$.
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