Two hockey players bumps against each other while skating on the ice.
The hockey players are wearing helmets.
Not all hockey players wear helmets.
(x)
exists e1 x1 x2 x3.(n_player(x1) & of(x1,x2) & n_hockey(x2) & Theme(e1,x3) & Actor(e1,x1) & v_wear(e1) & n_helmet(x3))