Section CGDist1.
Variable cg : CGraph1.
Fixpoint ad_0_path_dist_1 (x y : ad) (l : list ad)
(n : nat) {struct n} : option D :=
if N.eqb x y
then Some Dz
else
match n with
| O => None
| S n' =>
match MapGet _ cg x with
| None => None
| Some edges =>
if ad_in_list x l
then None
else
let l' := x :: l in (* builds reverse path *)
all_min
(fun (z : ad) (d : D) =>
if ad_in_list z l'
then None
else Ddplus (ad_0_path_dist_1 z y l' n') d) edges
end
end.
Definition ad_0_path_dist (x y : ad) :=
ad_0_path_dist_1 x y nil (MapCard _ cg).
(*s Uses a set [s] of already visited nodes *)
Fixpoint ad_1_path_dist_1 (x y : ad) (s : FSet) (n : nat) {struct n} :
option D :=
if N.eqb x y
then Some Dz
else
match n with
| O => None
| S n' =>
match MapGet _ cg x with
| None => None
| Some edges =>
match MapGet _ s x with
| Some _ => None
| None =>
let s' := MapPut unit s x tt in
all_min
(fun (z : ad) (d : D) =>
match MapGet _ s' z with
| Some _ => None
| None => Ddplus (ad_1_path_dist_1 z y s' n') d
end) edges
end
end
end.
Definition ad_1_path_dist (x y : ad) :=
ad_1_path_dist_1 x y (M0 unit) (MapCard _ cg).

Lemma ad_1_path_dist_big_enough :
forall n : nat,
MapCard _ cg <= n ->
forall x y : ad, ad_1_path_dist x y = ad_1_path_dist_1 x y (M0 unit) n.