sentences:  Justice Marshall held that the participation interests exchanged by Cottage Savings and the other S&Ls were "materially different" because the loans involved were made to different obligors and secured by different properties.Even though the interests were "substantially identical" for the FHLBB's purposes, that did not mean they were not materially different for taxation purposes.Therefore, the exchange was a "disposition of property," Cottage Savings had realized a loss, and their deduction was appropriate.