The requirement of leaving forgotten grain from a field which one declares ownerless and then harvests: Nedarim 44b
What-ifs
Time-frame for revoking a declaration which revoked ownership of a field, before/after it is claimed by another: Nedarim 43b-45a
Time-frame for revoking a declaration which revoked ownership of a field, where he had declared that it would be ownerless for a specific, limited time: Nedarim 44a
The status of property which had been condemned for destruction because of a court's verdict, if the court's verdict is then nullified because of new information: Keritot 24a
The status of property which one person attempts to give to another, but the intended recipient declines to accept: Keritot 24a-b