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Indicates that the file copy should be recorded as an incremental backup at the specified level . While such activity offers opportunities for competitors to formulate legitimate joint positions on issues of common concern , because , by definition , a trade or professional association assembles a group of competitors to work together on common issues for their mutual benefit , and because the antitrust laws are designed to promote competition , not cooperation , among competitors , association activity can also present significant antitrust risks . In addition to the risk of actual conduct that violates the antitrust laws , the nature of trade and professional association activity can at times cause legal conduct to appear to be suspect under the antitrust laws . To select only one picture from the several being displayed , scroll until you select the desired picture and then press the Multi-Display button again.This will display the currently selected picture at full size . A single A6 record may include a complete IPv6 address , or a contiguous portion of an address and information leading to one or more prefixes . In a letter to Professor Hartwig dated October 21 , 1997 , President McNamara informed him that his faculty appointment would not be renewed beyond June 30 , 1999 .