The details and interpretation of the "warranty claim", or in other words the much discussed "claw back" mechanism struck between Commonwealth Bank and UK bank HBOS over the sale by the latter of Bankwest to CBA, is the centrepiece of the class action now initiated by aggrieved Bankwest business borrowers.The statement of claim filed with the Supreme Court of New South Wales in connection with the Bankwest class action yesterday may be a more considered presentation of analysis first prepared for the inquiry by the same law firm nine months ago for the Parliamentary Joint Committee on Corporations and Financial Services into the impairment of loans.Trevor Hall of Hall Partners, a Parramatta law firm, was the author of that submission (a piece of work described yesterday in a commentary in Banking Day as advancing an interpretation of events that was "inventive" and "weird").Like the earlier work, the statement of claim places emphasis on the refinancing arrangements by CBA for Bankwest wholesale debt and the actual flow of funds to outline what amounts to a form of "claw back' by CBA from HBOS, allegedly the motive for the impairment of many loans.The claim lays weight on the "attempted price reduction in respect of claims for inadequate impairment and provisioning of Bankwest loans."Commonwealth Bank have refuted corresponding claims many times, including earlier this month at the most recent hearing of the Joint Committee.Hall Partners yesterday wrote in the statement of claim that "the final purchase price paid for Bankwest meant that CBA secured a net gain on acquisition of approximately A$983 million, with the result that it could write off and / or provision approximately $1,878 billion in impaired loans without any negative impact on its future profitability at the consolidated level."The claim allows that the definition of the matters at stake in working out any damages requires expert help. The plaintiffs ask the court to appoint "an independent suitably qualified and experienced 'expert' accountant (at CBA's expense) to review the books and records of the bank for the purposes of establishing the significant costs savings achieved by the second defendant, and certain of the profits made by the bank."