have under the relevant state law. Specifically, § 544(a) grants the trustee the rights of avoidance of (1) a judicial lien creditor, (2) an unsatisfied lien creditor, and (3) a bona fide purchaser of real property. In practice these avoidance powers often overlap with preference and fraudulent transfer avoidance powers. The creditors Secured creditors whose security interests survive the commencement of the case may look to the property that is the subject of their security interests, after obtaining permission from the court (in the form of relief from the automatic stay). Security interests, created by what are called secured transactions, are liens on the property of a debtor. Unsecured creditors are generally divided into two classes: unsecured priority creditors and general unsecured creditors. Unsecured priority creditors are further subdivided into classes as described in the law. In some cases the assets of the estate are insufficient to pay all priority unsecured creditors in full; in such cases the general unsecured creditors receive nothing. Because of the priority and rank ordering feature of bankruptcy law, debtors sometimes collude with others (who may be related to the debtor) to prefer them, by for example granting them a security interest in otherwise unpledged assets. For this reason, the bankruptcy trustee is permitted to reverse certain transactions of the debtor within a period of time prior to the date of the bankruptcy filing. The time period varies depending on the relationship of the parties to the debtor and the nature of the transaction. In Chapters 7, 12, and 13, creditors must file a "proof of claim" to be paid. In a Chapter 11 case, a creditor is not required to file a proof of claim (that is, a proof of claim is "deemed filed") if the creditor's claim is listed on the debtor's bankruptcy schedules, unless the claim is scheduled as "disputed, contingent, or unliquidated". If the creditor's claim is not listed on the schedules in a Chapter 11 case, the creditor must file a proof of claim. Absolute priority A distinctive feature of U.S. bankruptcy law is the absolute priority rule, codified at 11 U.S.C. § 1129(b)(2)(B)(ii). The rule provides that "[w]ith respect to a class of unsecured claims . . . the holder of any claim or interest that is junior to the claims of such class will not receive or retain under the plan on account of such junior claim or