R. Yosi Bar R. Chanina says if two people make a Neder not to benefit from each other they may not borrow or lend to each other and they may not sell or buy from each other.
Abaye says if a person makes a Neder that his friend may not benefit from him they may not borrow or lend to each other and they may not sell or buy from each other. (1)
If someone made a Neder that he will never plow his field, if he usually plows the field himself it is forbidden for him to plow his field. (2)
If he normally has someone else plow the field for him it is forbidden for anyone to plow his field.
If a person makes a Neder that he will not benefit from his friend, if he does not have anything to eat his friend may go to his storekeeper and say that someone made a Neder not to benefit from him and he does not know what to do.
The storekeeper may give him food and then he may collect payment from the friend.
If he needed workers to build his house or to fix his fence the friend may go to the workers and says that someone made a Neder not to benefit from him and he does not know what to do.
The workers may build his house and they may collect payment from the friend.
If they are traveling together and he does not have anything to eat the friend may give a food item to another person as a gift and that person may then give it to the friend.
If there is no one else with them he should place it on a rock and say that it is Hefker, but R. Yosi disagrees.
R. Yochanan says that R. Yosi holds that Hefker is like a gift and it remains in the possession of the original owner until someone is Zocheh in it.
R. Yosi holds that if the friend was Mafkir his possession prior to the Neder the object of Hefker is not forbidden to the person making the Neder. (3)
If a Shechiv me'Ra gives some of his property to one servant and he then gives away all of his property to a second person the first person is Koneh but not the second person. (4)
Rava says that R. Yosi holds that one may not give to a person who made a Neder by means of Hefker because of a Gezeirah. (5)
If someone is Mafkir his field he may back out within the first three days.
A BIT MORE
1. His friend may not lend to him or sell to him because of a Gezeirah that he may borrow or buy from him.
2. However other people may plow his field. Since he normally plows the field himself his intention with the Neder is to prohibit it on himself not on anyone else.
3. Because when a person makes a Neder he does not have in mind items that are Hefker.
4. A Shechiv me'Ra who gives away all of his property may back out of the gift if he recovers from his illness. He may not back out from the gift to the first person, even if he recovers, since it is a partial gift, but he may back out of the gift of to the second person because he gave away all of his remaining property to the second person including the items that he already gave to the first person.
5. We are concerned that if we allow him to give it to his friend by means of Hefker he may end up giving it to him directly as a gift.