People rock crawl up a steep obstacle.
People slide over a surface.
If a surface is steep one can slide down.
exists s1 x1 x2 x3 x4.(a_topic(x1) & up(x1,x4) & n_obstacle(x4) & a_steep(s1) & Theme(s1,x4) & n_crawl(x1) & of(x1,x3) & n_rock(x3) & of(x1,x2) & n_people(x2))
exists x1 x2 x3.(a_topic(x1) & over(x1,x3) & n_surface(x3) & n_slide(x1) & of(x1,x2) & n_people(x2))