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., begin selling garments with a similar design, United filed 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.