System admin rights



I am system admin and I have some questions about my exact permissions.

Based on your documentation located at

a system admin can edit any users, including other system admins.

But, in reality, I can not delete other system admin ( the action is greyed ) and apparently, some of the role can not be removed:

So, as system admin, can I delete other system admins and/or remove the system admin role on other system admin ?