Kiddushin, Chapter 9, Mishnah 9. This mishnah deals with the force of rumors that circulate in a city regarding kiddushin and divorce - to what extent we must take them into account and act upon them.
"Yatza shemah ba'ir mekudeshes - harei zo mekudeshes":
A woman who until now was considered unmarried, and a rumor spread through the city that she had become betrothed to a certain man - we take the rumor into account out of doubt and added caution, and she is considered betrothed. She may not marry another man unless she receives a get from the man to whom she was betrothed.
The Gemara clarifies that a vague rumor is not enough; actual details must be reported:
That people saw specific details about the wedding and the like.
That the women are celebrating with her.
That people are saying among themselves that she had kiddushin today with a certain man.
"Yatza shemah ba'ir megureshes - harei zo megureshes":
If about that very same woman, as the Gemara explains - that is, the one about whom the report went out that she was betrothed - a report went out that she was divorced, she is considered divorced. We are permitted to assume that she was indeed divorced, because this is a case of "a report that carries its own refutation": the report and the thing that nullifies it came out together. Therefore she is treated as one who is no longer betrothed, but divorced.
The mishnah qualifies both of these rulings: "Uvilvad shelo yehei sham amtala" - provided that there is no amtala, meaning a claim or a consideration that undermines the force of that rumor.
"Eizo hi amtala?"
Regarding divorce: "Gireish ish peloni es ishto al tenai" - the report went out that the divorce was carried out on condition, and we do not necessarily know that the condition was fulfilled.
Regarding kiddushin: "Zarak lah kiddusheha, safek karov lo safek karov lah" - the report went out that he threw her the kiddushin money or the ring, and it is uncertain whether it landed closer to her or closer to him, as was explained earlier in the tractate regarding what is considered close and what is not.
This is an amtala that nullifies the report: once it is found, the report is no longer considered valid, and there is no need to take it into account.
In summary: In this mishnah we learned that a report that spread through the city about a woman's kiddushin is taken into account, and she is considered betrothed and is not permitted to another man without a get; and that a report that spread about that very same woman that she was divorced renders her divorced, by the principle of "a report that carries its own refutation." All this provided that there is no amtala, such as a divorce given on condition or a throwing of kiddushin where it is uncertain whether it was closer to him or to her - in which case the report is nullified and we do not act upon it.