Summary:
רש"י maintains that the חברים and פרסיים are from the same nation and that they settled in בבל when כורש conquered בבל. However תוספות maintains that they are two separate nations, and חברים came to בבל during the lifetime of ר' יוחנן .
Summary:
If we maintain לא גזרי גזירה לגזירה, the concern of שמא ישכח is that he may forget to put away the needle before שבת, and then he will forget that it is שבת.
A person should not stand in a רה"ר and drink in a רה"י, etc. - לא יעמוד אדם ברשות הרבים וישתה ברשות היחיד
Summary:
We do not permit handling objects in another רשות if the object is needed by the handler. Otherwise it is permitted. Swallowing an object is considered a הנחה just as writing is a הנחה for ink.