Three men on a dirty river.
Men are picking up litter at the beach.
While there can be a beach at a river, a person cannot physically be on the river and at the beach at the same time.
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_river(x2) & of(x2,x3) & n_dirty(x3) & n_man(x1) & card_eq_3(x1))
exists e1 s1 x1 x2 x3.(n_beach(x3) & at(e1,x3) & a_up(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_pick(e1) & n_litter(x2) & n_man(x1))