There is a man in suit speaking at a podium at a protest march.
no one is speaking at a protest
Man is speaking definitely implies that someone is speaking but not as mentioned that no one is.
exists p1 x1 x2 x3 x4 x5 x6.(at(p1,x5) & n_march(x5) & of(x5,x6) & n_protest(x6) & at(p1,x4) & n_podium(x4) & in(p1,x2) & n_speaking(x2) & of(x2,x3) & n_suit(x3) & exists x7.((x1 = x7) & n_man(x7)))
-exists e1 x1 x2.(at(e1,x2) & n_protest(x2) & Actor(e1,x1) & v_speak(e1) & n_one(x1))