A rock climber on a vertical cliff.
A person is a rock climbing.
A vertical cliff can only be made of rock, so if someone is on one then they are rock climbing.
exists s1 x1 x2 x3.(a_topic(x1) & on(x1,x3) & n_cliff(x3) & a_vertical(s1) & Theme(s1,x3) & n_climber(x1) & of(x1,x2) & n_rock(x2))
exists p1 x1.(exists e1 x2 x3.((x1 = x2) & Actor(e1,x3) & v_climb(e1) & (x2 = x3) & n_rock(x2)) & n_person(x1))