Four ballet dancers in black costumes are performing on a stage.
people are performing ballet
Ballet dancers are people and if they are performing it can be assumed they are performing ballet
exists e1 s1 x1 x2 x3 x4.(on(e1,x4) & n_stage(x4) & Actor(e1,x1) & v_perform(e1) & in(x1,x3) & n_costume(x3) & a_black(s1) & Theme(s1,x3) & n_dancer(x1) & of(x1,x2) & n_ballet(x2) & card_eq_4(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_perform(e1) & n_ballet(x2) & n_people(x1))