6.49 (1978)

Solved

Is the minimal condition for abelian normal subgroups inherited by subgroups of finite index? This is true for the minimal condition for (all) abelian subgroups (J. S. Wilson, Math. Z., 114 (1970), 19–21).

Progress

No, not always. Let $G = [(A \times B \times C \times D) \rtimes (\langle g \rangle \times \langle t \rangle)] \rtimes (Y \times \langle x \rangle)$, where $A, B, C, D, Y$ are quasicyclic $p$-groups, $x^2 = 1$, while $g$ and $t$ are of infinite order. Let $A = \bigcup_{n=1}^\infty \langle a_n \rangle$, $B = \bigcup_{n=1}^\infty \langle b_n \rangle$, $C = \bigcup_{n=1}^\infty \langle c_n \rangle$, $D = \bigcup_{n=1}^\infty \langle d_n \rangle$, $Y = \bigcup_{n=1}^\infty \langle y_n \rangle$ with $a_{n+1}^p = a_n$, $b_{n+1}^p = bn, c_{n+1}^p = cn, d_{n+1}^p = dn, y_{n+1}^p = y_n$. We impose the relations $[ABCD, Y] = [ABC, g] = [ABD, t] = 1$; $[x, g] = gt^{-1}$; $[x, a_n] = a_n b_n^{-1}$; $[x, c_n] = c_n d_n^{-1}$; $[g, d_n] = b_n$; $[t, c_n] = a_n$; $[y_n, g] = c_n$; $[y_n, t] = d_n$. Then all abelian normal subgroups of $G$ satisfy the minimal condition for subgroups. The subgroup $H = [(A \times B \times C \times D) \rtimes (\langle g \rangle \times \langle t \rangle)] \rtimes Y$ does not satisfy the minimal condition for abelian normal subgroups, since the subgroups $E_n = A \times B \times C \times \langle g^{2^n} \rangle$ are normal in $H$ and form a strictly decreasing chain. (S. A. Chechin, Abstracts of 15th All-USSR Algebraic Conf., Krasnoyarsk, 1979).

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