# T-group

From Encyclopedia of Mathematics

2020 Mathematics Subject Classification: *Primary:* 20E15 [MSN][ZBL]

A group $G$ in which normality is transitive: if $N$ is a normal subgroup of $G$, and $H$ is a normal subgroup of $N$, then $H$ is a normal subgroup of $G$. Equivalently, every subnormal subgroup of $G$ is normal in $G$. Every completely reducible group is a T-group; the dihedral group of order 8 is the smallest finite group that is not a T-group. A group is a T-group if and only if it is equal to its own Wielandt subgroup.

#### References

- Derek Robinson, "A Course in the Theory of Groups", Graduate Texts in Mathematics
**80**Springer (1996)**ISBN**0-387-94461-3 Zbl 0483.20001

**How to Cite This Entry:**

T-group.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=T-group&oldid=54540