Well dressed youth laugh about something in public.
The youth are laughing.
Both sentences say the youth are laughing at something.
exists e1 x1 x2 x3 x4.(a_topic(x1) & about(x1,x3) & in(x3,x4) & n_public(x4) & n_thing(x3) & n_laugh(x1) & of(x1,x2) & n_youth(x2) & Theme(e1,x1) & v_dress(e1) & r_well(x1))
exists e1 x1.(n_youth(x1) & Actor(e1,x1) & v_laugh(e1))