A man speaking at a conference.
A man is sleeping.
speaking and sleeping cannot be done at the same time
exists x1 x2 x3.(a_topic(x1) & at(x1,x3) & n_conference(x3) & n_speaking(x1) & of(x1,x2) & n_man(x2))
exists e1 x1.(Actor(e1,x1) & v_sleep(e1) & n_man(x1))