People sit on benches.
People are sitting.
the sitting people are on the benches
exists e1 x1 x2.(on(e1,x2) & n_bench(x2) & Actor(e1,x1) & v_sit(e1) & n_people(x1))
exists e1 x1.(Actor(e1,x1) & v_sit(e1) & n_people(x1))