Objectives
 - REMINDER:  If you are not 100% confident with linked lists,
   TRY TO RECREATE THE append(..) example from scratch before starting HW13.
 - Understand Element / list structure for HW13 /HW14

mu_check(parse_result.element.as_list -> next -> next -> element.as_list -> next -> next -> element.as_string[0] == '*')