(* Definition of the expandM modality *)
Definition knot_rel (k1 k2:knot) :=
let (n,f) := unsquash k1 in
let (n',f') := unsquash k2 in
n = n' /\ Rel assert f f'.

(* Definitions of the "ageable" operations *)
Axiom knot_level : forall (k:knot),
level k = fst (unsquash k).