A man rides a bike down a city street.
The man is wearing a helmet.
Wearing a helmet means nothing more than wearing a helmet.  We don't know why the man is wearing a helmet.
exists e1 x1 x2 x3 x4.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & down(x2,x3) & n_street(x3) & of(x3,x4) & n_city(x4) & n_bike(x2) & n_man(x1))
exists e1 x1 x2.(n_man(x1) & Theme(e1,x2) & Actor(e1,x1) & v_wear(e1) & n_helmet(x2))