ed constraints and hints such as "you must solve this recursively" or "you should not destructively modify the input list" or "you do not have to handle the case when the string is empty" or "this operation must run in constant time". You may want to underline or highlight these instructions to be sure you don't overlook them. These constraints are not intended to make things difficult, typically we are trying to guide you in the direction of a straightforward and simple solution.  If you disregard these in