A girl on a bike stops to look back.
A girl looks back while sitting on her bicycle.
Sitting on a bicycle and being on a bike mean the same thing.
exists e1 p1 x1 x2.(Topic(e1,p1) & Actor(e1,x1) & v_stop(e1) & exists e2 p2.(exists s1.(Theme(s1,x1) & a_back(s1)) & Topic(e2,p2) & Actor(e2,x1) & v_look(e2)) & on(x1,x2) & n_bike(x2) & n_girl(x1))
exists e1 e2 p1 x1 x2.(while(e1,e2) & on(e2,x2) & n_bicycle(x2) & of(x2,x1) & n_female(x1) & Actor(e2,x1) & v_sit(e2) & exists s1.(Theme(s1,x1) & a_back(s1)) & Topic(e1,p1) & Actor(e1,x1) & v_look(e1) & n_girl(x1))