A group of people stand in the back of a truck filled with cotton.
Aliens are buying all the cotton.
A group of people does not equate to aliens. Standing in a truck doesn't mean that the persons are engaging in the act of buying.
exists e2 e1 x1 x2 x3 x4 x5 x6.(n_back(x3) & in(e1,x3) & of(x3,x4) & with(e2,x6) & n_cotton(x6) & Theme(e2,x5) & v_fill(e2) & (x4 = x5) & n_truck(x4) & Actor(e1,x1) & v_stand(e1) & of(x1,x2) & n_people(x2) & n_group(x1))
exists x1 x3.(n_cotton(x3) & all x2.((x2 = x3) -> exists e1.(Theme(e1,x2) & Actor(e1,x1) & v_buy(e1))) & n_alien(x1))