A young man stands on a roof.
A man working on a roof.
People go on roofs for reasons other than working on the roof.
exists e1 s1 x1 x2.(on(e1,x2) & n_roof(x2) & Actor(e1,x1) & v_stand(e1) & n_man(x1) & a_young(s1) & Theme(s1,x1))
exists e1 x1 x2 x3.(a_topic(x1) & on(e1,x3) & n_roof(x3) & Actor(e1,x2) & v_work(e1) & (x1 = x2) & n_man(x1))