People riding their bikes on a trail.
People are walking next to their bikes on the sidewalk
People can't be riding bikes and walking at the same time.
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(e1,x4) & n_trail(x4) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_bike(x3) & of(x3,x1) & n_thing(x1) & (x1 = x2) & n_people(x1))
exists e1 x1 x2 x3.(n_sidewalk(x3) & on(e1,x3) & to(e1,x2) & n_bike(x2) & of(x2,x1) & n_thing(x1) & r_next(e1) & Actor(e1,x1) & v_walk(e1) & n_people(x1))