The hikers descend on the mountain.
Some hikers are outdoors.
Some hikers outdoors are descending on the mountain.
exists e1 x1 x2.(n_mountain(x2) & n_hiker(x1) & on(e1,x2) & Actor(e1,x1) & v_descend(e1))
exists p1 x1.(exists x2.((x1 = x2) & n_outdoors(x2)) & n_hiker(x1))