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 approx_approx2 : forall m n, approx n = approx (m+n) oo approx n.