Chapter 10! A new mishnah - on the way documents are formally signed the details of their contracts within confirmed. With 2 kinds of documents - "regular" and "tied" - the signatures need to be as required for the details of the document itself to be valid. Plus, the need for 2 witnesses vs. 3 witnesses. Also, a discussion (by Jeremiah) of the Babylonian siege of the destruction of Jerusalem (the first time), God promises the return to the land - and the encouragement is buying land with documents so they have proof of purchase when they come back. These source verses are in the Prophets, which leads to the details they teach being rabbinic, as compared to a Torah verse. The bound documents merit their own additional scrutiny - unless they were common, or common for certain kinds of things. Also - how the signatures on the "tied" document worked (machloket!).