Responsa for Yevamot 214:11

כדתניא בית שמאי אומרים בפני בית דין וב"ה אומרים בפני בית דין ושלא בפני בית דין ואלו ואלו מודים שצריך שלשה רבי יוסי בר יהודה ורבי אלעזר ברבי שמעון מכשירין בשנים אמר רב יוסף בר מניומי אמר רב נחמן הלכה כאותו הזוג:

and others said: [Even] R. Assi.<span class="x" onmousemove="('comment',' Much more so R. Oshaia (v. supra n. 13). Even R. Assi who, unlike R. Oshaia agrees with R. Johanan in permitting the marriage of a minor, after her mi'un, only where the number of levirs is more than one, differs, nevertheless, from him in allowing the minor to marry the very levir against whom her declaration of refusal was made. ');">²⁹</span> BETH SHAMMAI RULED&nbsp;… IN HIS PRESENCE etc. It was taught: Beth Hillel said to Beth Shammai, 'Did not the wife of Pishon the camel driver make her declaration of refusal in his absence?' 'Pishon the camel driver', answered Beth Shammai to Beth Hillel, 'used a reversible measure;<span class="x" onmousemove="('comment',' [H] (rt. [H] 'to bend' [H], a measure of capacity having a deep receptacle at one end and a shallow one at the other, to defraud thereby sellers and buyers; 'a false measure'. This is a metaphor expressing Pishon's double dealing with his wife in pretending merely to eat the fruit of her melog property, to which he was in fact entitled, while in reality he was encroaching upon the property itself which belonged to her. ');">³⁰</span> they, therefore, used against him also a reversible measure'.<span class="x" onmousemove="('comment',' He was paid 'measure for measure', 'tit for tat'. In other cases, however, mi'un must be declared before Beth din only. ');">³¹</span> Since, however, he was eating the usufruct<span class="x" onmousemove="('comment',' Of the minor's melog property. ');">³²</span>

Teshuvot Maharam