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 unage_join2 :
forall z x' y' z', join x' y' z' -> age z z' ->
exists x, exists y, join x y z /\ age x x' /\ age y y'.