A man performing stunts on a snowboard.
A man is performing stunts while on a snowboard.
On a snowboard and while on a snowboard mean the same.
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(e1,x4) & n_snowboard(x4) & Theme(e1,x3) & Actor(e1,x2) & v_perform(e1) & n_stunt(x3) & (x1 = x2) & n_man(x1))
exists e1 x1 x2 x3.(on(e1,x3) & n_snowboard(x3) & r_while(e1) & Theme(e1,x2) & Actor(e1,x1) & v_perform(e1) & n_stunt(x2) & n_man(x1))