(*s Computing the minimum of edges in a Map *)
Definition all_min (f : ad -> D -> option D) := MapFold _ _ None Ddmin f.

Lemma all_min_le_2 :
forall (f : ad -> D -> option D) (m : Map D) (d : D),
all_min f m = Some d ->
{a : ad &  {d' : D | MapGet _ m a = Some d' /\ f a d' = Some d}}.