A snowboarder crashes into another.
A skiier does not crash into anything.
A skier does not have to be a snowboarder.  Someone either crashes into something or not.
exists e1 x1 x2.(into(e1,x2) & n_thing(x2) & Actor(e1,x1) & v_crash(e1) & n_snowboarder(x1))
exists x1.(-exists e1.(all x2.(n_thing(x2) -> into(e1,x2)) & Actor(e1,x1) & v_crash(e1)) & n_skiier(x1))