People are waiting by the curb.
There are people at the curb.
people are waiting at the curb is same as by waiting by the curb
exists e1 x1 x2.(n_curb(x2) & by(e1,x2) & Actor(e1,x1) & v_wait(e1) & n_people(x1))
exists p1 x1 x3.(n_curb(x3) & exists x2.((x1 = x2) & at(x2,x3) & n_people(x2)))