Construction workers building a railroad.
Workers are building a house.
One cannot build  a railroad and a house simultaneously.
exists e1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_build(e1) & n_railroad(x3) & n_worker(x1) & of(x1,x2) & n_construction(x2))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_build(e1) & n_house(x2) & n_worker(x1))