Now that we’re well (and sadly?) past the era of composers’ cutting contests, where the likes of Beethoven would take a theme from a pretender and improvise a dazzling set of variations (the origin of the finale of the “Eroica” symphony), it is exceedingly, impossibly rare to witness what I heard in December. Early in the month, the American Modern Ensemble played a concert at the DiMenna Center for Classical Music. The program was based around music from Robert Paterson’s terrific recent recording, Winter Songs, made with the same ensemble. The concert was bookended by Paterson’s CAPTCHA and the title