People on bikes gathered at night.
people riding bikes.
The people must be riding the bikes if they are on them.
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(x1,x2) & at(e1,x4) & n_night(x4) & Theme(e1,x3) & v_gather(e1) & (x2 = x3) & n_bike(x2) & n_people(x1))
exists e1 x1 x2 x3.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_ride(e1) & n_bike(x3) & (x1 = x2) & n_people(x1))