Normal not implies normal-potentially characteristic

From Groupprops
Revision as of 12:52, 23 April 2009 by Vipul (talk | contribs) (Created page with '{{subgroup property non-implication| stronger = normal subgroup| weaker = semi-strongly potentially characteristic subgroup}} ==Statement== ===Verbal statement=== It is possib...')
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

This article gives the statement and possibly, proof, of a non-implication relation between two subgroup properties. That is, it states that every subgroup satisfying the first subgroup property (i.e., normal subgroup) need not satisfy the second subgroup property (i.e., semi-strongly potentially characteristic subgroup)
View a complete list of subgroup property non-implications | View a complete list of subgroup property implications
Get more facts about normal subgroup|Get more facts about semi-strongly potentially characteristic subgroup

EXPLORE EXAMPLES YOURSELF: View examples of subgroups satisfying property normal subgroup but not semi-strongly potentially characteristic subgroup|View examples of subgroups satisfying property normal subgroup and semi-strongly potentially characteristic subgroup

Statement

Verbal statement

It is possible to have a normal subgroup of a group that is not a semi-strongly potentially characteristic subgroup.

Statement with symbols

We can have a group K with a subgroup H such that H is normal in K, but whenever G is a group containing K as a normal subgroup, H is not a characteristic subgroup in G.

Facts used

  1. Normal-extensible not implies normal

Proof

By fact (1), we can find a group K, a normal subgroup H of K, and a normal-extensible automorphism σ of K such that σ(H)H. Thus, for any group G containing K as a normal subgroup, σ extends to an automorphism σ of G. But then, σ(H)=σ(H)H, so H is not characteristic in G.