People are waiting by the curb.
People wait at a bus stop.
Not all curbs have bus stops located on them.
exists e1 x1 x2.(n_curb(x2) & by(e1,x2) & Actor(e1,x1) & v_wait(e1) & n_people(x1))
exists e1 x1 x2 x3.(at(e1,x2) & n_stop(x2) & of(x2,x3) & n_bus(x3) & Actor(e1,x1) & v_wait(e1) & n_people(x1))