In October 2008, Delta Air Lines completed its acquisition of Northwest Airlines. The newly merged company is the largest airline in the world. The following statement regarding the merger is from a Justice Department press release: After a thorough, six-month investigation, during which the [Antitrust] Division obtained extensive information from a wide range of market participants-including the companies, other airlines, corporate customers and travel agents-the Division has determined that the proposed merger between Delta and Northwest is likely to produce substantial and credible efficiencies that will benefit U.S. consumers and is not likely to substantially lessen competition. What does the Justice Department mean by "substantial and credible efficiencies," and how might they benefit U.S. consumers? Why would a merger between two large airlines not be "likely to substantially lessen competition"?