Before us is Mishnah 5 in chapter 7 of Tractate Gittin, which deals with a divorce given on condition: from when does the divorce take effect, and how do we rule when the woman is prevented from fulfilling the condition.
The words of the Mishnah:
"Harei zeh gitech al menas shetitni li masayim zuz - harei zo megureshes v'siten" - a man who gives his wife a get and stipulates with her that she give him two hundred zuz, she is divorced from the moment the get was given, provided that she fulfills the condition and actually gives him the two hundred zuz.
By contrast, when the husband uses a different wording: "al menas shetitni li mikan v'ad sheloshim yom - im nasnah lo b'soch sheloshim yom megureshes, v'im lo einah megureshes" - here the husband set a time frame. If she gave him the two hundred zuz within thirty days, the divorce takes effect; if she did not give it, the get does not take effect.
The Gemara's completion of the wording of the Mishnah:
At this point the Gemara notes that several words are missing from the Mishnah, and this is how its text should read: he said to his wife "Harei zeh gitech al menas shetitni li itztalisi" - an itztalis is a kind of long, distinctive cloak - provided that she gives it to him, and then she will be divorced. But it happened that "avdah itztalito" - his cloak was lost. How do we rule in such a case?
The first Tanna: she is not divorced. The husband asked for one specific item, and once it was lost and she can no longer fulfill the condition, the get is null and void.
Rabban Shimon ben Gamliel: "titen lo es dameha" - the condition can be fulfilled with monetary compensation, since the husband did not intend that particular item alone, but rather the item or its value.
The incident in Tzaidan:
The Mishnah brings a proof for this position: "Amar Rabban Shimon ben Gamliel: ma'aseh b'Tzaidan b'echad she'amar l'ishto harei zeh gitech al menas shetitni li itztalisi, v'avdah itztalito, v'amru chachamim titen lo es dameha" - in a place called Tzaidan an incident occurred involving a man who gave his wife a get on condition that she give him his cloak, and the cloak was lost. The Sages ruled that she should give him its value in money, and that is sufficient.
This incident supports the view of Rabban Shimon ben Gamliel and not the view of the first Tanna: giving the monetary compensation fulfills the condition, and therefore the get is valid.
In summary: in this Mishnah we learned the laws of a get given on condition - in the wording "harei zo megureshes v'siten," where the divorce takes effect from the moment of the giving and the condition is fulfilled afterward, and in the wording that sets a time limit of thirty days, where the divorce depends on the condition being fulfilled within that period. We also examined the Gemara's completion of the text regarding the cloak that was lost, the dispute between the first Tanna and Rabban Shimon ben Gamliel as to whether the condition can be fulfilled through payment of its value, and the incident in Tzaidan that supports the view of Rabban Shimon ben Gamliel.