A large group of people fill a street.
the crowd is a mob
A large group of people does not imply a mob.
exists e1 s1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_fill(e1) & n_street(x3) & of(x1,x2) & n_people(x2) & n_group(x1) & a_large(s1) & Theme(s1,x1))
exists p1 x1.(n_crowd(x1) & exists x2.((x1 = x2) & n_mob(x2)))