
A group \(G\) is said to have the \(n\)-rewritable property \(Q_n\) if for all elements \(g_1,g_2,\dots,g_n\in G\), there exist two distinct permutations \(\sigma\) and \(\tau\in\text{Sym}_n\) such that \[ g_{\sigma(1)}g_{\sigma(2)}\cdots g_{\sigma(n)}=g_{\tau(1)}g_{\tau(2)}\cdots g_{\tau(n)}. \] For a group \(G\), \(\Delta(G)\) is the set of elements \(g\in G\) whose centralizers in \(G\) have finite index. \(\Delta(G)\) is a characteristic subgroup of \(G\). The main results of the paper under review are the following: Theorem 1.1. Let \(G\) be a group satisfying the rewritable property \(Q_n\). Then \(G\) has a characteristic subgroup \(N\), contained in \(\Delta(G)\), such that \(|G:N|\) and \(|N'|\) are finite and have sizes bounded by functions of \(n\). A group \(G\) is said to have the \(n\)-permutational property \(P_n\) if for all elements \(g_1,g_2,\dots,g_n\in G\), there exists a nonidentity permutation \(\sigma\in\text{Sym}_n\) such that \[ g_1g_2\cdots g_n=g_{\sigma(1)}g_{\sigma(2)}\cdots g_{\sigma(n)}. \] It is clear that \(Q_n\subseteq P_n\) for all \(n>1\). The following result shows that there exists a function \(f\colon\mathbb N\to\mathbb N\) such that \(P_n\subset Q_{f(n)}\). Corollary 1.3. If \(G\) satisfies the rewritable property \(Q_n\), then \(G\) satisfies the permutational property \(P_m\) with \(m\) bounded by a function of \(n\). The authors of the paper under review introduce a generalization of \(n\)-permutational groups as follows. Let \(m\) and \(n\) be positive integers and suppose that \(\mathcal A\) is a set of \(n\)-tuples \((a_1,a_2,\dots,a_n)\) of elements of \(G\) with \(|\mathcal A|=m\). A group \(G\) is said to be \((m,n)\)-permutational with respect to \(\mathcal A\) if for every \(n\)-tuple \((x_1,x_2,\dots,x_n)\) of elements of \(G\) there exist an \(n\)-tuple \((a_1,a_2,\dots,a_n)\in\mathcal A\) and a nonidentity permutation \(\sigma\in\text{Sym}_n\) such that \[ x_1a_1x_2a_2\cdots x_na_n=x_{\sigma(1)}a_{\sigma(1)}x_{\sigma(2)}a_{\sigma(2)}\cdots x_{\sigma(n)}a_{\sigma(n)}. \] For a group \(G\) and each integer \(k\), \(\Delta_k(G)\) denotes the set \(\{x\in G\mid |G:C_G(x)|\leq k\}\). The proof of the following result uses arguments as that of Theorem 2.6 of the paper under review. Proposition 4.1. If \(G\) is an \((m,n)\)-permutational group with respect to \(\mathcal A\), then setting \(k=m\cdot n!\), we have (i) \(|G:\Delta_k(G)|\leq k\cdot(k+1)!\), and (ii) \(G\) has a characteristic subgroup \(N\) with \(|G:N|\leq k\cdot (k+1)!\), and with \(|N'|\) finite and bounded by a function of \(n\). In the last section of the paper under review the authors discuss known results on group algebras satisfying a polynomial identity. Let \(K\) be a field and let \(\mathcal F=K\langle\zeta_1,\zeta_2,\zeta_3,\dots\rangle\) be the free \(K\)-algebra in the noncommuting variables \(\zeta_1,\zeta_2,\zeta_3,\dots\). A \(K\)-algebra \(R\) is said to satisfy the polynomial identity \(f(\zeta_1,\zeta_2,\dots,\zeta_k)\in\mathcal F\) if \(f(r_1,r_2,\dots,r_k)=0\) for all \(r_1,r_2,\dots,r_k\in R\). The main similarity between algebras satisfying a polynomial identity and permutational groups is perhaps Lemma 5.1 of the paper saying that every \(K\)-algebra \(R\) satisfying a polynomial identity of degree \(n\), satisfies a multilinear identity of the form \[ f(\zeta_1,\zeta_2,\dots,\zeta_n)=\sum_{\sigma\in\text{Sym}_n} k_\sigma\zeta_{\sigma(1)}\zeta_{\sigma(2)}\cdots\zeta_{\sigma(n)}, \] with \(k_\sigma\in K\) and \(k_1=1\).
Generators, relations, and presentations of groups, characteristic subgroups, Algebra and Number Theory, Group rings, group algebras, FC-groups and their generalizations, rewritable groups, Group algebras, Subgroup theorems; subgroup growth, finite conjugate center, rewriting properties, Polynomial identities, polynomial identities, permutation properties, Finite conjugate center, Permutational groups, Rewritable groups, combinatorial conditions on subsets, Local properties of groups, permutational groups
Generators, relations, and presentations of groups, characteristic subgroups, Algebra and Number Theory, Group rings, group algebras, FC-groups and their generalizations, rewritable groups, Group algebras, Subgroup theorems; subgroup growth, finite conjugate center, rewriting properties, Polynomial identities, polynomial identities, permutation properties, Finite conjugate center, Permutational groups, Rewritable groups, combinatorial conditions on subsets, Local properties of groups, permutational groups
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