This show started innocently enough. Four Denver-area songwriters were booked to perform a Saturday night at The Walnut Room. But somewhere along the way, the lighthearted singer John Common, guitarist Jen Korte, sweet-voiced Ellison Park, and mellow rocker Corey Teruya decided to turn their performance into a competition. According to them, four performers will enter, but only one will leave. Sat, Mar. 21, 8 p.m., The Walnut Room, 3131 Walnut St. 303-292-1700, $10