T-group

This article defines a group property: a property that can be evaluated to true/false for any given group, invariant under isomorphism
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History

Origin

The notion of T-group was introduced by Derek J.S. Robinson in his paper A Note on Finite Groups in which normality is transitive published in 1968.

Definition

Symbol-free definition

A group is termed a T-group if any subnormal subgroup of the group is normal in the group. In other words, a T group is a group such that any normal subgroup of a normal subgroup of it is normal in it.

Definition with symbols

A group $G$ is termed a T-group if whenever $H$ is normal in $G$ and $K$ is normal in $H$ , $K$ is also normal in $G$ .

In terms of the subgroup property collapse operator

This group property can be defined in terms of the collapse of two subgroup properties. In other words, a group satisfies this group property if and only if every subgroup of it satisfying the first property ({{{1}}}Property "Defining ingredient" (as page type) with input value "{{{1}}}" contains invalid characters or is incomplete and therefore can cause unexpected results during a query or annotation process.) satisfies the second property ({{{2}}}Property "Defining ingredient" (as page type) with input value "{{{2}}}" contains invalid characters or is incomplete and therefore can cause unexpected results during a query or annotation process.), and vice versa.
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The property of being a T-group can be viewed as any of these subgroup property collapses:

The collapse transitively normal subgroup = normal subgroup
The collapse normal subgroup = subnormal subgroup

Relation with other properties

Stronger properties

Conjunction with other properties

nilpotent T-group which is the same as Dedekind group

Weaker properties

HN-group (when we are working with finite groups)

Metaproperties

Quotients

This group property is quotient-closed, viz., any quotient of a group satisfying the property also has the property
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Any quotient of a T-group is a T-group. This follows from the fact that a subgroup in the quotient is normal if and only if its full inverse image is normal in the original group.

Effect of property operators

Subgroup-closure

The property of being a group such that every subgroup of it is a T-group, is termed the property of being a T*-group.

References

A Note on Finite Groups in which normality is transitive by Derek J.S. Robinson, Proceedings of the Americal Mathematical Society Vol. 19 No. 4, Aug 1968, Page 933-937

External links

JSTOR link for Robinson's paper: Access restricted to subscribers