People in costumes are standing outside.
Nobody was allowed to wear a costume.
People who are in costumes have clearly been allowed to wear them, which 'nobody allowed to wear costume' contradicts.
exists e1 s1 x1 x2.(a_outside(s1) & Manner(e1,s1) & Actor(e1,x1) & v_stand(e1) & in(x1,x2) & n_costume(x2) & n_people(x1))
-exists e1 p1 x1.(Recipient(e1,p1) & Topic(e1,x1) & v_allow(e1) & exists e2 x2.(Theme(e2,x2) & Actor(e2,x1) & v_wear(e2) & n_costume(x2)) & n_person(x1))