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\(C\)-normality of groups and its properties. (English) Zbl 0847.20010
A subgroup \(H\) of finite group \(G\) is called \(c\)-normal in \(G\) if there exists a normal subgroup \(N\) of \(G\) such that \(G=HN\) and \(H\cap N\leq H_G\), the normal core of \(H\) in \(G\). The author derives several results relating the structure of \(G\) and its \(c\)-normal maximal subgroups. Theorem 3.1. \(G\) is solvable if and only if every maximal subgroup of \(G\) is \(c\)-normal in \(G\). Theorem 3.2. A maximal subgroup \(M\) of \(G\) is \(c\)-normal in \(G\) if and only if \(\eta(G:M)\), the normal index of \(M\) in \(G\), \(=[G:M]\). Theorem 4.1. \(G\) is supersolvable if \(P_1\) is \(c\)-normal in \(G\) for every maximal subgroup \(P_1\) of each Sylow subgroup \(P\) of \(G\).

20D10 Finite solvable groups, theory of formations, Schunck classes, Fitting classes, \(\pi\)-length, ranks
20D25 Special subgroups (Frattini, Fitting, etc.)
20D35 Subnormal subgroups of abstract finite groups
20D40 Products of subgroups of abstract finite groups
20E28 Maximal subgroups
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