The company's repertoire is now so rich its spring concerts feature two completely different programs except for one overlap. The dancers are superb, particularly Peter Gaona, Jeanette Gordon, and veteran Paul Christiano. Once it masters unison dancing it will be truly astonishing, and even now it's a pleasure to watch in Jon Lehrer's demanding Iambus and Melissa Thodos's world premiere, Rituals--a kinder, gentler Rite of Spring. The fewer dancers, though, the better: Amy Ernst's charming duet Raft (a company premiere on both programs) sparkles, making creative use of turntables as one woman partners another. And Saturday's program includes a company-premiere duet for men, Brock Clawson's marvelous Glitch, whose romantic moves are periodically "rewound"--the dancers repeat them backward--suggesting the missteps on the way to coupled bliss. Showcasing Chicago's current profusion of choreographic talent, these concerts are a wonderful celebration of birth and renewal. Program A: Sat 3/12, 8 PM. Program B: Fri 3/11, 8 PM, Sun 3/13, 3 PM. Harold Washington Library Center, auditorium, 400 S. State, 312-266-6255. $25-$30.