People riding their bikes on a trail.
People are on bikes
you are on bikes if people are riding their bikes
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 p1 x1.(exists x2.(on(x1,x2) & n_bike(x2)) & n_people(x1))