a biker rides down the street.
The biker is a man
Not all bikers are a man.
exists e1 x1 x2.(n_street(x2) & down(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_biker(x1))
exists p1 x1.(n_biker(x1) & exists x2.((x1 = x2) & n_man(x2)))