A lot of people wearing helmet are riding bikes on a trail.
People riding bikes on trail.
Both sentences explain that the people are riding bikes on a trail.
exists e2 e1 x1 x2 x3 x4 x5 x6.(on(e2,x6) & n_trail(x6) & Theme(e2,x5) & Actor(e2,x1) & v_ride(e2) & n_bike(x5) & of(x1,x2) & Theme(e1,x4) & Actor(e1,x3) & v_wear(e1) & n_helmet(x4) & (x2 = x3) & n_people(x2) & n_lot(x1))
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) & (x1 = x2) & n_people(x1))