A group of people are riding in the back of a truck.
People are on a truck.
people are riding in the back of a truck. shows that people are on a a truck.
exists e1 x1 x2 x3 x4.(n_back(x3) & in(e1,x3) & of(x3,x4) & n_truck(x4) & Actor(e1,x1) & v_ride(e1) & of(x1,x2) & n_people(x2) & n_group(x1))
exists p1 x1.(exists x2.(on(x1,x2) & n_truck(x2)) & n_people(x1))