There is a red truck behind the horses.
The horses are being transported on a float towed by a red truck.
A truck could be behind horses for a reason other than being transported. A truck does not always tow a float.
exists p1 x1 x3.(n_horse(x3) & exists s1 x2.((x1 = x2) & behind(x2,x3) & n_truck(x2) & a_red(s1) & Theme(s1,x2)))
exists e1 e2 s1 x1 x2 x3 x4.(n_horse(x1) & on(e1,x2) & Actor(e2,x4) & n_truck(x4) & a_red(s1) & Theme(s1,x4) & Theme(e2,x3) & v_tow(e2) & (x2 = x3) & n_float(x2) & Theme(e1,x1) & v_transport(e1))