Questions:Characteristic subgroup

This is a questions page on characteristic subgroup, listing common questions that may occur both to people encountering the definition for the first time and to people who have spent some time with the definition.

In addition to reading these questions, you should read: characteristic subgroup (the main page on the topic).

Also see facts about characteristic subgroups, facts that prove that a subgroup is characteristic, and facts that use that a subgroup is characteristic.