A group of people riding on motorcycles down the road wearing helmets.
The group is in a gang
You can not infer they are in the gang.
exists e1 e2 x1 x2 x3 x4 x5 x6 x7.(n_road(x5) & a_topic(x1) & of(x1,x2) & down(e1,x5) & Theme(e2,x7) & Actor(e2,x6) & v_wear(e2) & n_helmet(x7) & (x5 = x6) & on(e1,x4) & n_motorcycle(x4) & Actor(e1,x3) & v_ride(e1) & (x2 = x3) & n_people(x2) & n_group(x1))
exists p1 x1.(n_group(x1) & exists x2.(in(x1,x2) & n_gang(x2)))