Malnormal subgroup
In mathematics, in the field of group theory, a subgroup 
of a group 
is termed malnormal if for any 
in but not in , and 
intersect in the identity element.
Some facts about malnormality:
- An intersection of malnormal subgroups is malnormal.
- Malnormality is transitive, that is, a malnormal subgroup of a malnormal subgroup is malnormal.
- The trivial subgroup and the whole group are malnormal subgroups. A normal subgroup that is also malnormal must be one of these.
- Every malnormal subgroup is a TI subgroup.