A boy is going down the slide.
A boy is on a slide
If he is going down the slide, he is on a slide.
exists e1 s1 x1 x2.(n_slide(x2) & a_down(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_go(e1) & n_boy(x1))
exists p1 x1.(exists x2.(on(x1,x2) & n_slide(x2)) & n_boy(x1))