A man is cleaning the walkway at an airport.
A man is cleaning a dirty walkway at an airport.
Just because he is cleaning it, doesn't necessarily mean that the walkway is dirty.
exists e1 x1 x2 x3.(n_walkway(x2) & Theme(e1,x2) & Actor(e1,x1) & v_clean(e1) & at(x2,x3) & n_airport(x3) & n_man(x1))
exists e1 x1 x2 x3 x4.(Theme(e1,x2) & Actor(e1,x1) & v_clean(e1) & at(x2,x4) & n_airport(x4) & n_walkway(x2) & of(x2,x3) & n_dirty(x3) & n_man(x1))