Definition stratify (n:nat) : { x:sinv n | stratifies n x }.

(* Specifications: *)
Lemma decompose_nat : forall (x y:nat), { m:nat & y = (m + S x) } + { ge x y }.
Lemma decompose_nat : forall (x y:nat), { m:nat & y = (m + S x) } + { ge x y }.
Lemma decompose_nat : forall (x y:nat), { m:nat & y = (m + S x) } + { ge x y }.