Someone is riding a three-wheeled vehicle throught a sandy playground.
The little boy is riding a tricycle.
A someone is not necessarily a little boy.
exists x1.(all x3 x2.((n_playground(x2) & of(x2,x3) & n_sandy(x3)) -> exists e1 s1 x4 x5.(Theme(e1,x4) & Actor(e1,x1) & v_ride(e1) & for(x4,x2) & n_throught(x4) & of(x4,x5) & n_vehicle(x5) & a_three-wheeled(s1) & Theme(s1,x4))) & n_person(x1))
exists e1 s1 x1 x2.(n_boy(x1) & a_little(s1) & Theme(s1,x1) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_tricycle(x2))