A girl is in the surf.
The girl is surfing.
If the girl is in the surf then she is not on the surf-surfing.
exists p1 x1 x2.(n_surf(x2) & in(x1,x2) & n_girl(x1))
exists e1 x1.(n_girl(x1) & Actor(e1,x1) & v_surf(e1))