“After You” is a dance of civil behavior, of good manners that include good humor. Its courtesy is the courtesy of ballet, of orderly entrances and exits and the sharing of stage space, but also of classical music. The music is the piano septet in C by Johann Neopuk Hummel, a student of Mozart and contemporary of Beethoven. Apart from its inclusion of a trumpet in a chamber setting (the source of the septet’s “military” label), the score is conventional, distinguished mainly by the balance among its instruments, politely passing around thematic material like dishes at a dinner party. Even the trumpet is modest. It is this balance that Mr. Morris mirrors.