diff --git a/lib/sasacore/sasa.ml b/lib/sasacore/sasa.ml
index b598862cf0f51358ca4044b11a96413ebc29d6b5..7fbc91594c5e5a7e7612e53c7aa12910c54c1063 100644
--- a/lib/sasacore/sasa.ml
+++ b/lib/sasacore/sasa.ml
@@ -1,4 +1,4 @@
-(* Time-stamp: <modified the 20/03/2019 (at 12:09) by Erwan Jahier> *)
+(* Time-stamp: <modified the 22/03/2019 (at 09:44) by Erwan Jahier> *)
 
 (* XXX Je pourrais utiliser Lwt pour rendre step non-bloquant, ce qui
    permettrait d'accelerer la simu sur les machines qui ont plusieurs
@@ -21,15 +21,13 @@ let (update_env_with_init : Env.t -> Process.t list -> Algo.neighbor list list -
     in
     List.fold_left2 aux e pl neighbors
     
-let (get_neighors: Process.t -> Topology.neighbor list) =
-  fun p ->
+let (get_neighors: Topology.t -> Process.t -> Topology.neighbor list) =
+  fun g p ->
     let id = p.Process.pid in
-    let idl = try Hashtbl.find Topology.node_succ id with Not_found -> [] in
+    let idl = g.succ id in
     List.map
       (fun id ->
-         let node =
-           try Hashtbl.find Topology.node_info id with Not_found -> assert false
-         in
+         let node = g.of_id id in
          let algo_id = Filename.chop_suffix node.file ".cmxs" in
           {
             Topology.n_id = node.id;
@@ -154,7 +152,8 @@ let (make : string array -> t) =
     in
     try
     let dot_file = args.topo in
-    let nl = Topology.read dot_file in
+    let g = Topology.read dot_file in
+    let nl = g.nodes in
     let nstrl = List.map (fun n -> n.Topology.id) nl in
     let nstr = String.concat "," nstrl in
     Algo.verbose_level := args.verbose;
@@ -162,7 +161,7 @@ let (make : string array -> t) =
     if !Algo.verbose_level > 0 then Printf.eprintf "nodes: %s\nedges:\n" nstr;
     let e = Env.init () in
     let pl = List.map (Process.make (args.demon=Custom)) nl in
-    let neighors = List.map get_neighors pl in
+    let neighors = List.map (get_neighors g) pl in
     let algo_neighors = List.map (List.map (to_algo_neighbor e)) neighors in
     let e = update_env_with_init e pl algo_neighors in
     let pl_n = List.combine pl neighors in
diff --git a/lib/sasacore/topology.ml b/lib/sasacore/topology.ml
index acb62645fc4ac4fce1ed17bf59a2c59edb476b64..b54bc7b3577c3a43228443f3a230c4da13d18113 100644
--- a/lib/sasacore/topology.ml
+++ b/lib/sasacore/topology.ml
@@ -1,4 +1,4 @@
-(* Time-stamp: <modified the 13/03/2019 (at 14:49) by Erwan Jahier> *)
+(* Time-stamp: <modified the 22/03/2019 (at 09:40) by Erwan Jahier> *)
 
 open Graph
 open Graph.Dot_ast
@@ -12,7 +12,11 @@ type node = {
 
 type edge = node_id * node_id list
 
-type t = node list
+type t = {
+  nodes: node list;
+  succ: node_id -> node_id list;
+  of_id: node_id -> node;
+}
 
 type node_info_t = (string, node) Hashtbl.t
 let node_info:node_info_t = Hashtbl.create 100
@@ -109,7 +113,13 @@ let (read: string -> t) = fun f ->
   let dot_file = Graph.Dot.parse_dot_ast f in
   assert (not dot_file.strict);
   let res = List.fold_left (do_stmt dot_file.digraph) [] dot_file.stmts in
-  List.rev res
+  {
+    nodes = List.rev res;
+    succ = (fun str -> try Hashtbl.find node_succ str with Not_found -> []);
+    of_id = (fun str -> try Hashtbl.find node_info str with Not_found ->
+        failwith (str^ " unknown node id")
+      )
+  }
 
 type neighbor = {
   n_id:  string;
diff --git a/lib/sasacore/topology.mli b/lib/sasacore/topology.mli
index 7acc5f157fbf6074a9db8334f6b8bd77d4c216b9..eddd2205a8d0d3e5992b3cc95645d11c694fce9c 100644
--- a/lib/sasacore/topology.mli
+++ b/lib/sasacore/topology.mli
@@ -1,4 +1,4 @@
-(* Time-stamp: <modified the 18/02/2019 (at 15:31) by Erwan Jahier> *)
+(* Time-stamp: <modified the 22/03/2019 (at 09:36) by Erwan Jahier> *)
 
 type node_id = string
 type node = {
@@ -9,7 +9,6 @@ type node = {
 
 type edge = node_id * node_id list
 
-type t = node list
 
 (* neighbor view from the sasa: in Algo.neighbor we hide the pid and
    compute the lenv *)
@@ -18,14 +17,11 @@ type neighbor = {
   n_vars: (string * Algo.varT) list;
 }
 
-type node_info_t = (string, node) Hashtbl.t
-val node_info : node_info_t 
-
-type node_succ_t = (string, string list) Hashtbl.t
-val node_succ : node_succ_t 
+type t = {
+  nodes: node list;
+  succ: node_id -> node_id list;
+  of_id: node_id -> node;
+}
 
-(** Parse a dot file 
-XXX side effect: and fills the node_info and node_succ tables 
-XXX good idea ?
-*)
+(** Parse a dot file *)
 val read: string -> t