You cannot see Agon, the summit of the George Balanchine-Igor Stravinsky collaboration, too many times. Revolutionary when it premiered in 1957, essays about its serialism and symbolism just keep coming. The title, ancient Greek for “contest” or “struggle,” becomes clear in the pas de deux, a tight-rope journey into the question, Who is in control? Agon shares the program with Jerome Robbins’s Glass Pieces (1983) and William Forsythe’s In the Middle, Somewhat Elevated (1987). —L.J.