A boy is rock climbing.
A boy is climbing rocks.
Rock climbing and climbing rocks is the same expression.
exists p1 x1.(exists x2 x3.((x1 = x2) & n_climb(x2) & of(x2,x3) & n_rock(x3)) & n_boy(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_climb(e1) & n_rock(x2) & n_boy(x1))