Farmer walking in his fields.
A farmer is riding a tractor.
Either the farmer is walking or he is riding. He cannot physically do both simultaneously.
exists x1 x2 x3.(a_topic(x1) & in(x1,x3) & n_field(x3) & of(x3,x1) & n_male(x1) & n_walking(x1) & (x1 = x2) & ne_tim_farmer(x2))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_tractor(x2) & n_farmer(x1))