Gittin 32 - Shabbat June 17, 28 Sivan

How does a husband cancel a get? At what stage can it be canceled? Originally he could cancel the get (before it reached the wife) by going in front of the beit din but Rabban Gamliel instituted a takana that one could no longer cancel the get in that way, as the wife may not hear the get was canceled and would think she was divorced. Which wording is effective and which wording would not be effective to cancel? If he cancels the get that a messenger is sending, can he reuse the same get later if he decides later to divorce his wife or is the get itself canceled, meaning did he just cancel the messenger or did he cancel the get as well?