A guy is doing a skateboard trick over stairs.
A guy in a black shirt is skateboarding.
guy  doesn't always mean black shirt
exists e1 x1 x2 x3 x4.(Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & over(x2,x4) & n_stair(x4) & n_trick(x2) & of(x2,x3) & n_skateboard(x3) & n_guy(x1))
exists e1 s1 x1 x2.(Actor(e1,x1) & v_skateboard(e1) & in(x1,x2) & n_shirt(x2) & a_black(s1) & Theme(s1,x2) & n_guy(x1))