A person with long hair is sitting on a purple couch.
A person is sitting down
the sentence does not need to be explained, the person is sitting down.
exists e1 s1 s2 x1 x2 x3.(on(e1,x3) & n_couch(x3) & a_purple(s2) & Theme(s2,x3) & Actor(e1,x1) & v_sit(e1) & with(x1,x2) & n_hair(x2) & a_long(s1) & Theme(s1,x2) & n_person(x1))
exists e1 s1 x1.(a_down(s1) & Manner(e1,s1) & Actor(e1,x1) & v_sit(e1) & n_person(x1))