A police officer riding a motorcycle.
There is a police officer riding a motorcycle.
police officer riding  can also be said as  There is a police officer riding
exists e1 x1 x2 x3 x4.(a_topic(x1) & Theme(e1,x4) & Actor(e1,x3) & v_ride(e1) & n_motorcycle(x4) & (x1 = x3) & n_officer(x1) & of(x1,x2) & n_police(x2))
exists p1 x1 e1 x2 x3 x4 x5.((x1 = x2) & Theme(e1,x5) & Actor(e1,x4) & v_ride(e1) & n_motorcycle(x5) & (x2 = x4) & n_officer(x2) & of(x2,x3) & n_police(x3))