The decree of the marketplace - takanat ha-shuk. Where something stolen in the marketplace leads to ye'ush (despair) and new ownership, and difficulty in requiring payback by the new owner to the original owner. Also, a new mishnah - when one has a barrel of wine and another has a barrel of honey, and the wine owner pours out the wine to offer the barrel to the slavage the honey. That wine owner can't claim the honey owner owes him for the wine, unless there was a stipulation and agreement in advance. Also, donkeys crossing a river, where one leaves his own donkey to help save the other more expensive donkey....