A woman and boy sit on a police motorcycle.
A boy and his mom are waiting for the policeman to return to his motorcycle.
A woman sitting on the same motorcycle as a boy doesn't have to be his mom. People can sit on a police motorcycle even if they aren't waiting for the policeman to return.
exists e1 x1 x2 x3 x4 x5.(on(e1,x4) & n_motorcycle(x4) & of(x4,x5) & n_police(x5) & Actor(e1,x1) & v_sit(e1) & n_boy(x3) & n_woman(x2) & subset_of(x3,x1) & subset_of(x2,x1))
exists e1 p1 x1 x2 x3 x4 x5.(n_policeman(x4) & Topic(e1,p1) & Actor(e1,x1) & v_wait(e1) & exists e2.(to(e2,x5) & Actor(e2,x4) & v_return(e2)) & n_motorcycle(x5) & of(x5,x2) & n_male(x2) & n_male(x2) & subset_of(x3,x1) & n_mom(x3) & of(x3,x2) & subset_of(x2,x1) & n_boy(x2))