Definition knot_rel (k1 k2:knot) :=
    let (n,f) := unsquash k1 in
    let (n',f') := unsquash k2 in
    n = n' /\ KI.Rel predicate f f'.

Lemma pred_ext : forall (p1 p2:predicate), (forall x, proj1_sig (bij_f _ _ KO.pkp p1) x = proj1_sig (bij_f _ _ KO.pkp p2) x) -> p1 = p2.