Four men do repair work on a roof.
Four men repair a roof because they are contractors.
The four men repairing a roof aren't necessarily contractors.
exists e1 x1 x2 x3 x4.(Theme(e1,x2) & Actor(e1,x1) & v_do(e1) & on(x2,x4) & n_roof(x4) & n_work(x2) & of(x2,x3) & n_repair(x3) & n_man(x1) & card_eq_4(x1))
exists e1 p1 x1 x2.(exists p2 x3.((x1 = x3) & n_contractor(x3)) & n_thing(x1) & because(e1,p1) & Theme(e1,x2) & Actor(e1,x1) & v_repair(e1) & n_roof(x2) & n_man(x1) & card_eq_4(x1))