Recently, a food retailer called Whole Foods sought to purchase Wild Oats, a competitor in the market for organic foods. When the Federal Trade Commission (FTC) sought to block this merger on antitrust grounds, FTC officials argued that such a merger would dramatically increase concentration in the market for "premium organic foods." Whole Foods' counterargument was that it considered itself to be part of the broadly defined supermarket industry that includes retailers such as Albertson's, Kroger, and Safeway. What key issue of antitrust regulation was involved in this dispute? Explain.