A fireman is on the roof of the house.
A fireman is swimming in a pool.
If a fireman is swimming in a pool, he can't be on the roof of a house.
exists p1 x1 x2 x3.(n_house(x3) & n_roof(x2) & on(x1,x2) & of(x2,x3) & n_fireman(x1))
exists e1 x1 x2.(in(e1,x2) & n_pool(x2) & Actor(e1,x1) & v_swim(e1) & n_fireman(x1))