Instance Canc_knot(Canc_F: forall A, Canc_alg (F A)) : Canc_alg knot.Instance Disj_knot(Disj_F: forall A, Disj_alg (F A)) : Disj_alg knot.

Lemma age_join2 : forall x y z z' : K'.knot, join x y z -> age z z' -> exists x' : K'.knot, exists y' : K'.knot, join x' y' z' /\ age x x' /\ age y y'.