Acquiring Metaltelin via Shtar and the Mitoch Principle in Shichrur

Description

The question is how the Gemara in Gittin 8b can hold that writing all one's property to a slave frees him, given that metaltelin cannot be acquired through a shtar and the mitoch principle should invalidate even the land transfer. The Chasam Sofer rejects proposed solutions via agav karka or chatzer as insufficient for this case, and tentatively proposes that since it is common knowledge that documents cannot acquire metaltelin, the situation resembles 'k'nei ata v'chamor,' where the kinyan is understood to apply only to the valid portion and mitoch does not apply.