snowboarders sit on a chairlift.
They are snowboarding
We don't know that the people are snowboarding.
exists e1 x1 x2.(on(e1,x2) & n_chairlift(x2) & Actor(e1,x1) & v_sit(e1) & n_snowboarder(x1))
exists e1 x1.(n_thing(x1) & Actor(e1,x1) & v_snowboard(e1))