People gathered for a presentation.
Some people running in a event.
People who are running in an event are not gathered for a presentation.
exists e1 x1 x2.(for(e1,x2) & n_presentation(x2) & Actor(e1,x1) & v_gather(e1) & n_people(x1))
exists e1 x1 x2 x3.(a_topic(x1) & in(e1,x3) & n_event(x3) & Actor(e1,x2) & v_run(e1) & (x1 = x2) & n_people(x1))