(* OK, GIVES THE "SMALLEST" INDICE j ST zj = zi: *)
Definition modulo(m:fmap)(z:dart)(i:dart)
(hi:inv_hmap m)(he:exd m z):nat.
(* REFLEXIVITY: *)

(* Specifications: *)
Lemma expo_refl:
forall(m:fmap)(z:dart), exd m z -> expo m z z.