Boy slam dunks a basketball.
The girl is dunking a basketball.
A boy is not a girl so the sentences are not talking about the same person.
exists e1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_dunk(e1) & n_basketball(x3) & n_slam(x1) & (x1 = x2) & ne_nam_boy(x2))
exists e1 x1 x2.(n_girl(x1) & Theme(e1,x2) & Actor(e1,x1) & v_dunk(e1) & n_basketball(x2))