1.
Eli asks:
Is this din that one partner can force the other one to do split the chetzer or field etc a din mideorisa or a takanas chachamim and do you know if any rishonim discuss it?
Eli, Usa
2.
The Kollel replies:
Dear Eli,
Both opinions exist. The Mabit in Kiryas Sefer (Shechenim 1) learns that it is d'Oraisa. The Rosh (Teshuvos 98:7) appears to explain that it is mid'Rabanan. From the Rashba (Teshuvos 1:956, 2:241) it seems that the right of splitting generally is d'Oraisa and prohibiting splitting when the item is too small is mid'Rabanan. See Chazon Ish (Bava Basra 6:17, 8:1). See more in Mesivta edition, Bava Basra, in Yalkut Rishonim, DH Tzarich she'Yiheyeh, and DH Hasam she'Ein, pages 164-165 and footnotes 43-50.
All the best,
Reuven Weiner