(* 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'.

Axiom expandM_spec : forall k k' o o',
expandM (k,o) (k',o') = (knot_rel k k' /\ ORel o o').