Definition extendM : modality :=
  exist _ R_extends R_extends_valid_rel.Definition contractsM : modality :=
  exist _ R_contracts R_contracts_valid_rel.Notation "'%' e"  := (box extendM e)(at level 30, right associativity): pred.

Lemma value_knot_laterR : forall k k' v v', laterR (A:=world) (k,v) (k',v') <-> clos_trans _ age k k' /\ v = v'.