[If one said:] “Here is your get on condition that you serve my father,” [or] “on condition that you nurse my son,” how long must she nurse him? Two years; R' Yehudah says: Eighteen months. If the son died, or the father died, it is a get. [If he said:] “Here is your get on condition that you serve my father for two years,” [or] “on condition that you nurse my son for two years” —- and the son died, or the father died, or the father said: “I do not want you to serve me” when [he was] not in anger, it is not a get. Rabban Shimon ben Gamliel says: [In a case] like this it is a get.  A rule was stated by Rabban Shimon ben Gamliel: [In] any [case of an] impediment which is not because of her, it is a get.