Before us is Mishnah 3 in the fifth chapter of Maseches Nedarim, which deals with one who is forbidden by vow to derive benefit from his fellow - a person who vowed not to derive any benefit from his friend. The Mishnah discusses two matters: property of the one who imposed the vow that has been rented out to someone else, and the wording of the vow and its force once the object has left its owner's possession.
The first topic - a bathhouse and an olive press that were rented out:
"HaMuddar hana'ah mechavero, v'yesh lo merchatz u'veis hebad hamuskarim ba'ir" - Reuven vowed not to derive benefit from Shimon. Shimon owns a bathhouse and an olive press (an installation for pressing olives) in the city, and they are rented out to a third party, Levi, who leased them from him. The question is whether Reuven may benefit from that bathhouse or that olive press, since ownership belongs to Shimon while the actual use has been handed over to Levi.
"Im yesh lo bahen tefisas yad - assur; ein lo bahen tefisas yad - mutar" - it depends on the extent of Shimon's hold on the property: if he retains any connection to the bathhouse or the olive press, Reuven may not benefit from them; and if he has no hold on them at all, it is permitted.
What is this "tefisas yad," this retained hold?
A share in the profits: Shimon receives a percentage of the earnings of the bathhouse or the olive press.
A space that was not rented out: there remains an area in the bathhouse or the olive press that the owner did not rent out, but kept for himself.
It emerges that if Shimon retains any hold on the property, Reuven may not benefit from it. But if everything was rented out, and the owner does not receive a percentage of the profits but only a fixed payment, Reuven is permitted to benefit from the place.
The second topic - "your house" as opposed to "this house":
"Ha'omer lachavero: konam l'veischa she'ani nichnas, v'sadcha she'ani lokeach" - a person makes a vow using the term "konam," meaning that he forbids the item to himself for benefit as though it were a sacrifice, and he says that he will not enter his fellow's house and will not buy his field.
"Meis, o shemacharan l'acher - mutar" - if his fellow died and his relatives inherited the property, or if he sold it to another person, the vow is released: he may enter the house and he may buy the field. The reason is that at the time of the vow he made the prohibition dependent on the owner - "your house," "your field" - and once it is no longer his house and no longer his field, the definition of the prohibition has lapsed.
"Konam l'bayis zeh she'ani nichnas, sadeh zu she'ani lokeach" - here he formulated his vow differently, and forbade to himself the object itself: this house and this field.
"Meis, o shemacharan l'acher - assur" - if the owner died or sold the property to another, the prohibition remains in force. For he did not make the vow dependent on the owner and did not say "your house," but rather "this house," and therefore the house and the field remain forbidden to him even after they have left the possession of the one who owned them at the time of the vow.
In summary: in this Mishnah we learned two rules concerning one who is forbidden by vow to derive benefit. The first: regarding property of the one who imposed the vow that was rented out to another - if he retains a "tefisas yad" in it, such as a percentage of the profits or a space he did not rent out, it is forbidden to the one bound by the vow; and if he has no hold on it, it is permitted. The second: everything depends on the wording of the vow - one who vows concerning "your house" and "your field" made the prohibition dependent on the owner, so once he died or sold it to another the vow is released; whereas one who vows concerning "this house" and "this field" forbade the object itself, and the prohibition stands even after the property has left its owner's possession.