Richard wrote a song called "College Days." He copyrighted the composition and had it professionally printed. A couple years later he was attending a business meeting about 1500 miles from his home. While sitting in a nightclub, he heard a small local band perform a song called "College Memories." The music and words were extremely similar to his song. The composer of "College Memories" claims he never heard of Richard's song and that she is offended he would accuse her of stealing his work. If Richard wishes to sue for copyright infringement, he must prove what?