The Jordan-Hölder theorem states that the composition quotient groups belonging to two composition series
of a finite group are, apart from their sequence, isomorphic
in pairs. Put
and
.
In other words, if
|
(1)
|
is one composition series and
|
(2)
|
is another, then ,
and corresponding to any composition quotient group
, there is a composition quotient group
such that
|
(3)
|
This theorem was proven in 1869-1889.
The Jordan-Hölder theorem also applies to modules with a composition series. Any two such series have the same length, and their successive quotient modules are isomorphic up to order (Atiyah and Macdonald 1969, p. 77).