发帖
雷达卡
1. Introduction
If N is a nontrivial proper normal subgroup of a finite group G then N and G=N are
smaller than G. While it is false that G can be completely reconstructed from knowledge
of N and G=N (see Example 1.1 below), it is nevertheless a standard technique in finite
group theory to prove theorems about finite groups by induction on the size of the group
and thereby use information about the smaller groups N and G=N to say something about
G.
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