Following your suggestions I gave to a given role (A) the administer users' permission and gave it the desired Administer Users by Role permissions (edit and delete users with roles B and C).
All is working but if a user with role A try to create a new user he can't assign to him a role B or C because the checkboxes to choose the roles are missing.


maybe now I understand.
If I want to allow a user to create a role whithout giving him "administer permissions" I should use another module in conjunction with administer users by roles, e.g. Role Delegation Module.
That's true?