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 unsquash_approx : forall k n Fp, unsquash k = (n, Fp) -> Fp = fmap F (approx n) (approx n) Fp.