XRP Ledger (XRPL) developers are using mathematical proofs to verify its new lending market against insolvency, with Common Prefix formally testing the protocol since Sept. 17. The protocol research firm is using Lean 4, a theorem-proving language, to ensure the Lending Protocol cannot violate its accounting and safety rules. This effort follows the recent xrpld version 3.4.0 amendment, LendingProtocolV1_1, which introduces closed-ended lending vaults and cash-basis accounting, increasing the stakes for internal bookkeeping accuracy. Previous verification efforts by Common Prefix between February and April already uncovered and addressed several issues in earlier versions of the Lending Protocol.