Definition ss_ok (ss : SS.t) (interp: positive -> COLTpoint) :=
  forall s, SS.mem s ss = true ->
  forall p1 p2 p3, S.mem p1 s && S.mem p2 s && S.mem p3 s = true ->
    CTCol (interp p1) (interp p2) (interp p3).Definition sp_ok (sp : SP.t) (interp: positive -> COLTpoint) :=
  forall p, SP.mem p sp = true -> interp (fstpp p) <> interp (sndpp p).

Lemma ss_ok_empty : forall interp, ss_ok SS.empty interp.