Responsa for Bava Batra 316:3

<big><strong>מתני׳</strong></big> נפל הבית עליו ועל אמו אלו ואלו מודין שיחלוקו אמר ר"ע מודה אני בזו שהנכסים בחזקתן אמר לו בן עזאי על חלוקין אנו מצטערין אלא שבאת לחלק עלינו את השוין:

AND HIS MOTHER,<span class="x" onmousemove="('comment',' In her widowhood. Her heirs (e.g.. her brothers) plead that the son died first and that, consequently, his mother inherited his estate before she died, and they now inherit it from her, while his heirs (e.g., his paternal brothers) plead that the reverse had happened and that they, therefore, are entitled to the inheritance. ');">⁶</span> BOTH<span class="x" onmousemove="('comment',' Lit., 'these and these', Beth Shammai and Beth Hillel who are in disagreement on the cases in the Mishnah, supra 157a and 158a. ');">⁷</span> AGREE THAT [THE ESTATE IN DISPUTE] IS TO BE DIVIDED.<span class="x" onmousemove="('comment',' Unlike the case of a father and son (Mishnah supra 157a), where one party claims possession as heirs and the other as creditors, or the case of a husband and wife (Mishnah. supra 158a), where certain kinds of property are in the legal ownership of the husband while others are in that of the wife, the case in our Mishnah deals with claims both of which are of equal strength, both being based on the right of inheritance, the widow being acknowledged as the undisputed possessor of the estate, the only point in doubt being whether the one party or the other is to be heir. As the equality of the claims leaves the question of ownership in equal doubt on either side, both schools are of the unanimous opinion that the estate in dispute must be divided. ');">⁸</span>

Teshuvot Maharam