Deriving the kal va-chomer reasoning got the stringent and lenient cases in testimony - and the strength of 2 witnesses (against the statement of the main person in question, eg, a defendant), in establishing the need for the party in question to take an oath regarding his claim. Also, different ways that one can confirm a partial claim and deny the rest - what happens then? When must an oath be taken? When must one may back what they've said they've paid (or the rest of it)? Plus, what happens when part of the terms are about a loan of land and part is vessels or utensils - when oaths for the sake.of one's claim about the transfer of land are not in use, without much explanation.