This is much more general than the direct product of groups when thinking about the group extension problem, because with the direct product of groups, both subgroups of the larger group are necessarily also normal (trivial projection group homomorphism on either side).

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- Group | 0, 2k, 47
- Algebra | 0, 2k, 65
- Mathematics | 17, 10k, 239
- Ciro Santilli's Homepage | 238, 147k, 2k