A gang of people are performing on a street.
There is a flash mob on the street.
The gang of people doesn't necessarily imply a flash mob.
exists e1 x1 x2 x3.(on(e1,x3) & n_street(x3) & Actor(e1,x1) & v_perform(e1) & of(x1,x2) & n_people(x2) & n_gang(x1))
exists p1 x1 x4.(n_street(x4) & exists x2 x3.((x1 = x2) & on(x2,x4) & n_mob(x2) & of(x2,x3) & n_flash(x3)))