A motorcycle rider stands on top of his bike.
A woman is riding on the handlebars of a bike.
One cannot be riding on top of a bike and on the handlebars simultaneously. His refers to a man, not a woman.
exists e1 x1 x2 x3 x4.(on(e1,x3) & of(x3,x4) & n_bike(x4) & of(x4,x1) & n_male(x1) & n_top(x3) & Actor(e1,x1) & v_stand(e1) & n_rider(x1) & of(x1,x2) & n_motorcycle(x2))
exists e1 x1 x2 x3.(n_handlebars(x2) & on(e1,x2) & of(x2,x3) & n_bike(x3) & Actor(e1,x1) & v_ride(e1) & n_woman(x1))