United Fabrics International, Inc., bought a fabric design from an Italian designer and registered a copyright to it with the U.S. Copyright Office. When Macy's, Inc., began selling garments with a similar design, United led a copyright infringement suit against Macy's. Macy's argued that United did not own a valid copyright to the design and so could not claim infringement. Does United have to prove that the copyright is valid to establish infringement? Explain.