Isomorph-containing subgroup

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This article defines a subgroup property: a property that can be evaluated to true/false given a group and a subgroup thereof, invariant under subgroup equivalence. View a complete list of subgroup properties[SHOW MORE]

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Definition

QUICK PHRASES: contains all isomorphic subgroups, weakly closed in any ambient group

A subgroup $H$ of a group $G$ is termed an isomorph-containing subgroup if it satisfies the following equivalent conditions:

1. Whenever $K\le G$ is a subgroup of $G$ isomorphic to $H$, $K\le H$.
2. If $G$ is a subgroup of $L$, $H$ is weakly closed in $G$ with respect to $L$.

Equivalence of definitions

Further information: Isomorph-containing iff weakly closed in any ambient group

Examples

VIEW: subgroups of groups satisfying this property | subgroups of groups dissatisfying this property
VIEW: Related subgroup property satisfactions | Related subgroup property dissatisfactions

Relation with other properties

Stronger properties

Property	Meaning	Proof of implication	Proof of strictness (reverse implication failure)	Intermediate notions
isomorph-free subgroup	no other isomorphic subgroup (for a finite subgroup, and more generally, for a co-Hopfian subgroup, the two properties are equivalent)	obvious	any example of a non-co-Hopfian group as a subgroup of itself -- such as the group of integers
homomorph-containing subgroup	contains any homomorphic image of itself in the group	obvious; isomorphs are also homomorphic images	cyclic maximal subgroup of dihedral group:D8 is isomorph-containing but not homomorph-containing	|FULL LIST, MORE INFO
Subhomomorph-containing subgroup	contains any homomorphic image in the whole group of any subgroup of it	(via homomorph-containing)	(via homomorph-containing)	|FULL LIST, MORE INFO
subisomorph-containing subgroup	contains any subgroup of the whole group isomorphic to any subgroup of itself	(obvious)	cyclic maximal subgroup of dihedral group:D8 is isomorph-containing but not subisomorph-containing	|FULL LIST, MORE INFO
variety-containing subgroup	contains any subgroup of the whole group in the subvariety of the variety of groups generated by it	(obvious)	(via either homomorph-containing or subisomorph-containing)	|FULL LIST, MORE INFO
fully invariant direct factor	both a fully invariant subgroup and a direct factor	equivalence of definitions of fully invariant direct factor		|FULL LIST, MORE INFO

Weaker properties

Property	Meaning	Proof of implication	Proof of strictness (reverse implication failure)	Intermediate notions
characteristic subgroup	invariant under any automorphism of the whole group	isomorph-containing implies characteristic	characteristic not implies isomorph-containing	|FULL LIST, MORE INFO
injective endomorphism-invariant subgroup	invariant under any injective endomorphism of the whole group		Can use same example as for characteristic not implies isomorph-containing, if finite	|FULL LIST, MORE INFO	intermediately injective endomorphism-invariant subgroup	injective endomorphism-invariant in every intermediate subgroup			|FULL LIST, MORE INFO
intermediately characteristic subgroup	characteristic in every intermediate subgroup			|FULL LIST, MORE INFO
normal subgroup	invariant under all inner automorphisms			Characteristic subgroup|FULL LIST, MORE INFO
normal-isomorph-containing subgroup	contains any normal subgroup of the whole group isomorphic to it	(obvious)	any proper nontrivial subgroup of a finite simple non-abelian group	|FULL LIST, MORE INFO

Metaproperties

Transitivity

NO: This subgroup property is not transitive: a subgroup with this property in a subgroup with this property, need not have the property in the whole group
ABOUT THIS PROPERTY: View variations of this property that are transitive|View variations of this property that are not transitive
ABOUT TRANSITIVITY: View a complete list of subgroup properties that are not transitive|View facts related to transitivity of subgroup properties | View a survey article on disproving transitivity

For full proof, refer: Isomorph-containment is not transitive

Trimness

This subgroup property is trim -- it is both trivially true (true for the trivial subgroup) and identity-true (true for a group as a subgroup of itself).
View other trim subgroup properties | View other trivially true subgroup properties | View other identity-true subgroup properties

Intermediate subgroup condition

YES: This subgroup property satisfies the intermediate subgroup condition: if a subgroup has the property in the whole group, it has the property in every intermediate subgroup.
ABOUT THIS PROPERTY: View variations of this property satisfying intermediate subgroup condition | View variations of this property not satisfying intermediate subgroup condition
ABOUT INTERMEDIATE SUBROUP CONDITION:View all properties satisfying intermediate subgroup condition | View facts about intermediate subgroup condition