The rider skates down the stair rails.
There is a person riding down the stair rails.
The rider who skates down the stair rails is a person.
exists e1 s1 x1 x2 x3.(n_rail(x2) & of(x2,x3) & n_stair(x3) & n_rider(x1) & a_down(s1) & Manner(e1,s1) & Theme(e1,x2) & Actor(e1,x1) & v_skate(e1))
exists p1 x1 x4 x5.(n_rail(x4) & of(x4,x5) & n_stair(x5) & exists e1 s1 x2 x3.((x1 = x2) & a_down(s1) & Manner(e1,s1) & Theme(e1,x4) & Actor(e1,x3) & v_ride(e1) & (x2 = x3) & n_person(x2)))