Definition ss_ok (ss : SS.t) (interp: positive -> COINCpoint) :=
  forall s, SS.mem s ss = true ->
  forall cp, memCP cp s = true ->
    app coinc (interp_CP cp interp).

Lemma consHdInterpOK : forall (cp : cartesianPower positive 1) (x : tST) interp, consHeadCP (interp_CP cp interp) (interp_CP x interp) = interp_CP (consHeadCP cp x) interp.