refactor: add some gospel comments

lib/sasacore/topology.mli

-(* Time-stamp: <modified the 20/06/2023 (at 15:07) by Erwan Jahier> *)
+(* Time-stamp: <modified the 24/01/2024 (at 16:28) by Erwan Jahier> *)
 
 (** {1 Topology: internal representation of Graphs } *)
 
@@ -24,7 +24,12 @@ val read: string -> t
 
 (** {1 Various eponymous util functions } *)
 
+
 val to_adjacency: t -> bool array array
+(*@ a = to_adjacency t
+  t.directed=false -> forall i, j. a.(i).(j) = a.(j).(i)
+*)
+
 val to_distance: t -> int array array
 val get_nb_link: t -> int
 val get_mean_degree : t -> float
@@ -38,7 +43,11 @@ val get_height : t -> string -> int
 val get_level : t -> string -> int
 val get_parent : t -> string -> int option
 val get_subtree_size : t -> string -> int
+
 val get_degree: t -> int * int
+(*@ dmin, dmax = get_degree t
+    ensures 0 <= dmin <= dmax
+*)
 
 (**  [reply  g p  p_neighbor]  returns  the  channel number  that  let
    [p_neighbor] access to the content of  [p], if [p] is a neighbor of