Every finite group has a finite composition series

From Groupprops

This article gives the statement and possibly, proof, of an implication relation between two group properties. That is, it states that every group satisfying the first group property (i.e., finite group) must also satisfy the second group property (i.e., group of finite composition length)
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Statement

Every finite group G has a composition series of finite length, that is, a sequence

{e}H1H2HkG

where KH denotes that K is a proper normal subgroup of H, and no K exists such that HiKHi+1 for i=1,2,,k1.

That is, every finite group is a group of finite composition length.

Proof

Induction on |G|.

When |G|=1, the trivial composition series {e} is a composition series.

Otherwise, pick a proper normal subgroup HG with |H| maximal.

Then by induction, H has a composition series {e}H1H2HkH of finite length.

Then {e}H1H2HkHG is a composition series for G of finite length.