A group of people at a rodeo.
Someone is wearing a cowboy hat.
You can not infer there is someone.
exists x1 x2 x3.(a_topic(x1) & of(x1,x2) & at(x2,x3) & n_rodeo(x3) & n_people(x2) & n_group(x1))
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_wear(e1) & n_hat(x2) & of(x2,x3) & n_cowboy(x3) & n_person(x1))