Statement
It is possible to have a group
and normal subgroups
and
of
that are Series-equivalent subgroups (?) in the sense that
and
, but
and
are not automorphic subgroups -- in other words, there is no automorphism of
that sends
to
.
Related facts
Stronger facts
There are many slight strengthenings of the result that are presented below, along with the smallest order of known examples.
| Statement |
Constraint on  |
Smallest order of among known examples |
Isomorphism class of  |
Isomorphism class of  |
Isomorphism class of quotient group
|
| series-equivalent abelian-quotient abelian not implies automorphic |
and are both abelian |
16 |
nontrivial semidirect product of Z4 and Z4 |
direct product of Z4 and Z2 |
cyclic group:Z2
|
| series-equivalent characteristic central subgroups may be distinct |
and are both central subgroups of  |
32 |
SmallGroup(32,28) |
cyclic group:Z2 |
direct product of D8 and Z2
|
| series-equivalent abelian-quotient central subgroups not implies automorphic |
and are central and are abelian |
64 |
semidirect product of Z8 and Z8 of M-type |
direct product of Z4 and Z2 |
direct product of Z4 and Z2
|
| series-equivalent not implies automorphic in finite abelian group |
is a finite abelian group |
128 |
direct product of Z8 and Z4 and V4 |
direct product of Z8 and V4 |
direct product of Z4 and Z2
|
| characteristic maximal not implies isomorph-free in group of prime power order |
and are maximal, is characteristic, and is a group of prime power order |
16 |
nontrivial semidirect product of Z4 and Z4 |
direct product of Z4 and Z2 |
cyclic group:Z2
|
| characteristic maximal subgroups may be isomorphic and distinct in group of prime power order |
Both and are characteristic and maximal and is a group of prime power order |
64 |
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|
Proof
For the proof, see any of the stronger facts listed above.