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9.64 (1984)

Solved

Is it true that, in a group of the form $G = AB$, every subgroup $N$ of $A \cap B$ which is subnormal both in $A$ and in $B$ is subnormal in $G$? The answer is affirmative in the case of finite groups (H. Wielandt).

Contributor: Ya. P. Sysak

Progress

No, not always (C. Casolo, U. Dardano, J. Group Theory, 7 (2004), 507–520).

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