not paid; so as a matter of practical economics, if the downturn in a company's fortunes which resulted in bankruptcy makes the performance of an executory contract less valuable than its breach, the rational company would breach. There would be no negative monetary consequences of such breach because there would be no money left for the other contract party to take because in practice general unsecured creditors are left with nothing. In Bildisco, the Court also ruled that under the Bankruptcy Code as written at that time, an employer in Chapter 11 bankruptcy "does not commit an unfair labor practice when, after the filing of a bankruptcy petition but before court-approved rejection of the collective-bargaining agreement, it unilaterally modifies or terminates one or more provisions of the agreement." After the Bildisco decision, Congress amended the Bankruptcy Code by adding a subsection (f) to section 1113 (effective for cases that commenced on or after July 10, 1984): (f) No provision of this title shall be construed to permit a trustee to unilaterally terminate or alter any provisions of a collective bargaining agreement prior to compliance with the provisions of this section. According to commentator Nicholas Brannick, "Despite the appearance of protection for the PBGC's interest in the event of termination, the Bankruptcy Code frequently strips the PBGC of the protection provided under ERISA. Under ERISA, termination liability may arise on the date of termination, but the lien that protects the PBGC's interest in that liability must be perfected [to be protected in bankruptcy]." The retention of title as a security interest, the creation of lien, or any other direct or indirect mode of disposing of or parting with property or an interest in property is a "transfer" for purposes of the U.S. Bankruptcy Code (see ). Some transfers may be avoidable by the bankruptcy trustee under various Code provisions. Further, under ordinary principles of bankruptcy law, a lien or other security interest that is unperfected (i.e., a lien that is not valid against parties other than the debtor) at the time of case commencement is generally unenforceable against a bankruptcy trustee. Once the bankruptcy case has commenced, the law generally stays any act to attempt to perfect a lien that was not perfected prior to case commencement (see ). Thus, the PBGC with a lien that has not yet been perfected at the time of case commencement may find itself in