R. Eliezer says that a Yavam may annul the Neder of his Shomeres Yavam. (1)
R. Yehoshua says that if there is only one Yavam he may annul the Neder of his Shomeres Yavam. (2)
R. Akiva says that a Yavam may not annul the Neder of a Shomeres Yavam.
R. Eliezer and R. Yehoshua hold Yesh Zikah and R. Akiva holds Ein Zikah. (3)
Beis Shamai holds that Ma'amar is a complete Kinyan. (4)
If the first Yavam does Ma'amar the second Yavam may invalidate her on the first Yavam by giving a Get or doing a Bi’ah.
R. Elazar holds that even according to Beis Shamai Ma'amar is only Koneh to push off the Tzarah. (5)
If the Yavam is taken to Beis Din and he runs away he is obligated to provide Mezonos to the Shomeres Yavam.
Rabah asks if Ma'amar according to Beis Shamai makes an Erusin or Nisu’in.
A BIT MORE
1. Even if there is more than one Yavam.
2. Because R. Yehoshua Yesh Zikah.
3. Zikah means that the Yevamah has the same attachment to the Yavam as an Arusah or a Nesu’ah.
4. Ma'amar means that the Yevamah received a Kidushin from the Yavam.
5. If two sisters are married to two brothers and one of the brothers dies and a third brother did Ma'amar to the Yevamah and subsequently the second Yavam dies the second Yevamah is free to get married without Chalitzah because she is the sister of the Ba'alas Ma'amar.