People are rollerskating in a roller rink.
The people are dancing on their rollerskates.
Just because people are rollerskating, it doesn't imply  they are dancing.
exists e1 x1 x2 x3.(in(e1,x2) & n_rink(x2) & of(x2,x3) & n_roller(x3) & Actor(e1,x1) & v_rollerskate(e1) & n_people(x1))
exists e1 x1 x2.(n_rollerskate(x2) & of(x2,x1) & n_thing(x1) & n_people(x1) & on(e1,x2) & Actor(e1,x1) & v_dance(e1))