Protesting youth relax in metro park, observed by armed police.
The police are alert.
observed by armed police implies the police are alert.
exists e2 e3 e1 s1 x1 x2 x3 x4.(for(e2,e3) & Actor(e3,x4) & n_police(x4) & a_armed(s1) & Theme(s1,x4) & Theme(e3,x1) & v_observe(e3) & in(e2,x2) & n_park(x2) & of(x2,x3) & n_metro(x3) & Actor(e2,x1) & v_relax(e2) & n_youth(x1) & Actor(e1,x1) & v_protest(e1))
exists s1 x1.(n_police(x1) & Theme(s1,x1) & a_alert(s1))