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'.