diff --git a/src/ace-lib/ace.ml b/src/ace-lib/ace.ml
index 8d2f8f0a6..2bbe01e06 100644
--- a/src/ace-lib/ace.ml
+++ b/src/ace-lib/ace.ml
@@ -1,6 +1,6 @@
 (* This file is part of Learn-OCaml.
  *
- * Copyright (C) 2019 OCaml Software Foundation.
+ * Copyright (C) 2019-2022 OCaml Software Foundation.
  * Copyright (C) 2016-2018 OCamlPro.
  *
  * Learn-OCaml is distributed under the terms of the MIT license. See the
@@ -20,6 +20,8 @@ type 'a editor = {
   editor: ('a editor * 'a option) Ace_types.editor Js.t;
   mutable marks: int list;
   mutable keybinding_menu: bool;
+  mutable synchronized : bool;
+  mutable sync_observers : (bool -> unit) list;
 }
 
 let ace : Ace_types.ace Js.t = Js.Unsafe.variable "ace"
@@ -30,10 +32,13 @@ let create_position r c =
   pos##.row := r;
   pos##.column := c;
   pos
+
 let greater_position p1 p2 =
   p1##.row > p2##.row ||
   (p1##.row = p2##.row && p1##.column > p2##.column)
 
+let register_sync_observer editor obs =
+  editor.sync_observers <- obs :: editor.sync_observers
 
 let create_range s e =
   let range : range Js.t = Js.Unsafe.obj [||] in
@@ -77,15 +82,37 @@ let get_contents ?range e =
       let r = create_range (create_position r1 c1) (create_position r2 c2) in
       Js.to_string @@ document##(getTextRange r)
 
-let create_editor editor_div =
+let set_synchronized_status editor status =
+  List.iter (fun obs -> obs status) editor.sync_observers;
+  editor.synchronized <- status
+
+let focus { editor } = editor##focus
+
+let create_editor editor_div check_valid_state =
   let editor = edit editor_div in
   Js.Unsafe.set editor "$blockScrolling" (Js.Unsafe.variable "Infinity");
   let data =
-    { editor; editor_div; marks = []; keybinding_menu = false; } in
+    { editor; editor_div;
+      marks = [];
+      keybinding_menu = false;
+      synchronized = true;
+      sync_observers = []
+    }
+  in
   editor##.customData := (data, None);
   editor##setOption (Js.string "displayIndentGuides") (Js.bool false);
+  editor##on (Js.string "change") (fun () ->
+      check_valid_state (set_contents data) (fun () -> focus data)
+        (fun () -> set_synchronized_status data true);
+      set_synchronized_status data false);
   data
 
+let set_synchronized editor =
+  set_synchronized_status editor true
+
+let is_synchronized editor =
+  editor.synchronized
+
 let get_custom_data { editor } =
   match snd editor##.customData with
   | None -> raise Not_found
@@ -168,7 +195,6 @@ let clear_marks editor =
 let record_event_handler editor event handler =
   editor.editor##(on (Js.string event) handler)
 
-let focus { editor } = editor##focus
 let resize { editor } force = editor##(resize (Js.bool force))
 
 let get_keybinding_menu e =
diff --git a/src/ace-lib/ace.mli b/src/ace-lib/ace.mli
index 6bc3b423e..6b922b2c1 100644
--- a/src/ace-lib/ace.mli
+++ b/src/ace-lib/ace.mli
@@ -17,7 +17,14 @@ type loc = {
   loc_end: int * int;
 }
 
-val create_editor: Dom_html.divElement Js.t -> 'a editor
+val create_editor: Dom_html.divElement Js.t
+  -> ((string -> unit) -> (unit -> unit) -> (unit -> unit) -> unit) -> 'a editor
+
+val is_synchronized : 'a editor -> bool
+
+val set_synchronized : 'a editor -> unit
+
+val register_sync_observer : 'a editor -> (bool -> unit) -> unit
 
 val set_mode: 'a editor -> string -> unit
 
diff --git a/src/ace-lib/ocaml_mode.ml b/src/ace-lib/ocaml_mode.ml
index c5bd1fecb..46278c8a7 100644
--- a/src/ace-lib/ocaml_mode.ml
+++ b/src/ace-lib/ocaml_mode.ml
@@ -514,8 +514,8 @@ let do_delete ace_editor =
     Ace.remove ace_editor "left"
   end
 
-let create_ocaml_editor div =
-  let ace = Ace.create_editor div in
+let create_ocaml_editor div check_valid_state =
+  let ace = Ace.create_editor div check_valid_state in
   Ace.set_mode ace "ace/mode/ocaml.ocp";
   Ace.set_tab_size ace !config.indent.IndentConfig.i_base;
   let editor = { ace; current_error = None; current_warnings = [] } in
diff --git a/src/ace-lib/ocaml_mode.mli b/src/ace-lib/ocaml_mode.mli
index d2d2f78f8..c86baae05 100644
--- a/src/ace-lib/ocaml_mode.mli
+++ b/src/ace-lib/ocaml_mode.mli
@@ -20,12 +20,12 @@ type msg = {
   msg: string;
 }
 
-
 type error = msg list
 
 type warning = error
 
-val create_ocaml_editor: Dom_html.divElement Js.t -> editor
+val create_ocaml_editor:
+  Dom_html.divElement Js.t -> ((string -> unit) -> (unit -> unit) -> (unit -> unit) -> unit) -> editor
 val get_editor: editor -> editor Ace.editor
 
 val report_error: editor -> ?set_class: bool -> error option -> warning list -> unit Lwt.t
diff --git a/src/app/learnocaml_common.ml b/src/app/learnocaml_common.ml
index cc8b4fcca..a7ccd0eb5 100644
--- a/src/app/learnocaml_common.ml
+++ b/src/app/learnocaml_common.ml
@@ -1,6 +1,6 @@
 (* This file is part of Learn-OCaml.
  *
- * Copyright (C) 2019 OCaml Software Foundation.
+ * Copyright (C) 2019-2020 OCaml Software Foundation.
  * Copyright (C) 2016-2018 OCamlPro.
  *
  * Learn-OCaml is distributed under the terms of the MIT license. See the
@@ -434,10 +434,13 @@ let get_state_as_save_file ?(include_reports = false) () =
     all_exercise_toplevel_histories = retrieve all_exercise_toplevel_histories;
   }
 
-let rec sync_save token save_file =
+let rec sync_save token save_file on_sync =
   Server_caller.request (Learnocaml_api.Update_save (token, save_file))
   >>= function
-  | Ok save -> set_state_from_save_file ~token save; Lwt.return save
+  | Ok save ->
+     set_state_from_save_file ~token save;
+     on_sync ();
+     Lwt.return save
   | Error (`Not_found _) ->
       Server_caller.request_exn
         (Learnocaml_api.Create_token ("", Some token, None)) >>= fun _token ->
@@ -445,19 +448,20 @@ let rec sync_save token save_file =
       Server_caller.request_exn
         (Learnocaml_api.Update_save (token, save_file)) >>= fun save ->
       set_state_from_save_file ~token save;
+      on_sync ();
       Lwt.return save
   | Error e ->
       lwt_alert ~title:[%i"SYNC FAILED"] [
         H.p [H.txt [%i"Could not synchronise save with the server"]];
         H.code [H.txt (Server_caller.string_of_error e)];
       ] ~buttons:[
-        [%i"Retry"], (fun () -> sync_save token save_file);
-        [%i"Ignore"], (fun () -> Lwt.return save_file);
+          [%i"Retry"], (fun () -> sync_save token save_file on_sync);
+          [%i"Ignore"], (fun () -> Lwt.return save_file);
       ]
 
-let sync token = sync_save token (get_state_as_save_file ())
+let sync token on_sync = sync_save token (get_state_as_save_file ()) on_sync
 
-let sync_exercise token ?answer ?editor id =
+let sync_exercise token ?answer ?editor id on_sync =
   let handle_serverless () =
     (* save the text at least locally (but not the report & grade, that could
        be misleading) *)
@@ -494,7 +498,7 @@ let sync_exercise token ?answer ?editor id =
   } in
   match token with
   | Some token ->
-     Lwt.catch (fun () -> sync_save token save_file)
+     Lwt.catch (fun () -> sync_save token save_file on_sync)
        (fun e ->
          handle_serverless ();
          raise e)
@@ -708,11 +712,72 @@ let mouseover_toggle_signal elt sigvalue setter =
   in
   Manip.Ev.onmouseover elt hdl
 
+(*
+
+   If a user has made no change to a solution for the exercise [id]
+   for 180 seconds, [check_valid_editor_state id] ensures that there is
+   no more recent version of this solution in the server. If this is
+   the case, the user is asked if we should download this solution
+   from the server.
+
+   This function reduces the risk of an involuntary overwriting of a
+   student solution when the solution is open in several clients.
+
+*)
+let is_synchronized_with_server_callback = ref (fun () -> false)
+
+let is_synchronized_with_server () = !is_synchronized_with_server_callback ()
+
+let check_valid_editor_state id =
+  let last_changed = ref (Unix.gettimeofday ()) in
+  fun update_content focus_back on_sync ->
+  let update_local_copy checking_time () =
+    let get_solution () =
+      Learnocaml_local_storage.(retrieve (exercise_state id)).Answer.solution in
+    try let mtime =
+          Learnocaml_local_storage.(retrieve (exercise_state id)).Answer.mtime in
+        if mtime > checking_time then begin
+          let buttons =
+            if is_synchronized_with_server () then
+              [
+                [%i "Fetch from server"],
+                (fun () -> let solution = get_solution () in
+                           Lwt.return (focus_back (); update_content solution; on_sync ()));
+                [%i "Ignore & keep editing"],
+                (fun () -> Lwt.return (focus_back ()));
+              ]
+            else
+              [
+                [%i "Ignore & keep editing"],
+                (fun () -> Lwt.return (focus_back ()));
+                [%i "Fetch from server & overwrite"],
+                (fun () -> let solution = get_solution () in
+                           Lwt.return (focus_back (); update_content solution; on_sync ()));
+              ]
+         in
+         lwt_alert ~title:"Question"
+           ~buttons
+           [ H.p [H.txt [%i "A more recent answer exists on the server. \
+                             Do you want to fetch the new version?"] ] ]
+          end else Lwt.return_unit
+    with
+    | Not_found -> Lwt.return ()
+  in
+  let now = Unix.gettimeofday () in
+  if now -. !last_changed > 180. then (
+    let checking_time = !last_changed in
+    last_changed := now;
+    Lwt.async (update_local_copy checking_time)
+  ) else
+    last_changed := now
+
+
 let ace_display tab =
   let ace = lazy (
     let answer =
       Ocaml_mode.create_ocaml_editor
         (Tyxml_js.To_dom.of_div tab)
+        (fun _ _ _ -> ())
     in
     let ace = Ocaml_mode.get_editor answer in
     Ace.set_font_size ace 16;
@@ -874,7 +939,8 @@ end
 
 module Editor_button (E : Editor_info) = struct
 
-  let editor_button = button ~container:E.buttons_container ~theme:"light"
+  let editor_button =
+    button ~container:E.buttons_container ~theme:"light"
 
   let cleanup template =
   editor_button
@@ -901,16 +967,26 @@ module Editor_button (E : Editor_info) = struct
       select_tab "toplevel";
       Lwt.return_unit
 
-  let sync token id =
-    editor_button
+  let sync token id on_sync =
+    let state = button_state () in
+    (editor_button
+      ~state
       ~icon: "sync" [%i"Sync"] @@ fun () ->
       token >>= fun token ->
-      sync_exercise token id ~editor:(Ace.get_contents E.ace) >|= fun _save -> ()
+      sync_exercise token id ~editor:(Ace.get_contents E.ace) on_sync
+      >|= fun _save -> ());
+    Ace.register_sync_observer E.ace (fun sync ->
+        if sync then disable_button state else enable_button state)
+
 end
 
-let setup_editor solution =
+let setup_editor id solution =
   let editor_pane = find_component "learnocaml-exo-editor-pane" in
-  let editor = Ocaml_mode.create_ocaml_editor (Tyxml_js.To_dom.of_div editor_pane) in
+  let editor =
+    Ocaml_mode.create_ocaml_editor
+      (Tyxml_js.To_dom.of_div editor_pane)
+      (check_valid_editor_state id)
+  in
   let ace = Ocaml_mode.get_editor editor in
   Ace.set_contents ace ~reset_undo:true solution;
   Ace.set_font_size ace 18;
@@ -1022,7 +1098,7 @@ let setup_prelude_pane ace prelude =
     (fun _ -> state := not !state ; update () ; true) ;
   Manip.appendChildren prelude_pane
     [ prelude_title ; prelude_container ]
-    
+
 let get_token ?(has_server = true) () =
   if not has_server then
     Lwt.return None
@@ -1041,7 +1117,7 @@ let get_token ?(has_server = true) () =
       >|= fun token ->
       Learnocaml_local_storage.(store sync_token) token;
       Some token
-      
+
 module Display_exercise =
   functor (
     Q: sig
diff --git a/src/app/learnocaml_common.mli b/src/app/learnocaml_common.mli
index 5ace9a36f..90d917aaa 100644
--- a/src/app/learnocaml_common.mli
+++ b/src/app/learnocaml_common.mli
@@ -119,18 +119,22 @@ val set_state_from_save_file :
 (** Gets a save file containing the locally stored data *)
 val get_state_as_save_file : ?include_reports:bool -> unit -> Save.t
 
-(** Sync the local save state with the server state, and returns the merged save
-    file. The save will be created on the server if it doesn't exist.
+(**
+    [sync token on_sync] synchronizes the local save state with the server state,
+    and returns the merged save file. The save will be created on the server
+    if it doesn't exist. [on_sync ()] is called when this is done.
 
-    This syncs student {b content}, but never the reports which are only synched
-    on "Grade" *)
-val sync: Token.t -> Save.t Lwt.t
+    Notice that this function synchronizes student {b,content} but not the
+    reports which are only synchronized when an actual "grading" is done.
+*)
+val sync: Token.t -> (unit -> unit) -> Save.t Lwt.t
 
 (** The same, but limiting the submission to the given exercise, using the given
     answer if any, and the given editor text, if any. *)
 val sync_exercise:
   Token.t option -> ?answer:Learnocaml_data.Answer.t -> ?editor:string ->
   Learnocaml_data.Exercise.id ->
+  (unit -> unit) ->
   Save.t Lwt.t
 
 val countdown:
@@ -211,10 +215,12 @@ module Editor_button (_ : Editor_info) : sig
   val cleanup : string -> unit
   val download : string -> unit
   val eval : Learnocaml_toplevel.t -> (string -> unit) -> unit
-  val sync : Token.t option Lwt.t -> Learnocaml_data.SMap.key -> unit
+  val sync : Token.t option Lwt.t -> Learnocaml_data.SMap.key -> (unit -> unit) -> unit
 end
 
-val setup_editor : string -> Ocaml_mode.editor * Ocaml_mode.editor Ace.editor
+val setup_editor : string -> string -> Ocaml_mode.editor * Ocaml_mode.editor Ace.editor
+
+val is_synchronized_with_server_callback : (unit -> bool) ref
 
 val typecheck :
   Learnocaml_toplevel.t ->
diff --git a/src/app/learnocaml_exercise_main.ml b/src/app/learnocaml_exercise_main.ml
index f0492a58b..bea8bde16 100644
--- a/src/app/learnocaml_exercise_main.ml
+++ b/src/app/learnocaml_exercise_main.ml
@@ -1,6 +1,6 @@
 (* This file is part of Learn-OCaml.
  *
- * Copyright (C) 2019 OCaml Software Foundation.
+ * Copyright (C) 2019-2020 OCaml Software Foundation.
  * Copyright (C) 2016-2018 OCamlPro.
  *
  * Learn-OCaml is distributed under the terms of the MIT license. See the
@@ -81,9 +81,9 @@ module Exercise_link =
         ]
         content
   end
-  
-module Display = Display_exercise(Exercise_link)    
-open Display  
+
+module Display = Display_exercise(Exercise_link)
+open Display
 
 let is_readonly = ref false
 
@@ -179,10 +179,11 @@ let () =
     Tyxml_js.Html5.[ h1 [ txt ex_meta.Exercise.Meta.title ] ;
                      Tyxml_js.Of_dom.of_iFrame text_iframe ] ;
   (* ---- editor pane --------------------------------------------------- *)
-  let editor, ace = setup_editor solution in
+  let editor, ace = setup_editor id solution in
+  is_synchronized_with_server_callback := (fun () -> Ace.is_synchronized ace);
   let module EB = Editor_button (struct let ace = ace let buttons_container = editor_toolbar end) in
   EB.cleanup (Learnocaml_exercise.(access File.template exo));
-  EB.sync token id;
+  EB.sync token id (fun () -> Ace.focus ace; Ace.set_synchronized ace) ;
   EB.download id;
   EB.eval top select_tab;
   let typecheck = typecheck top ace editor in
@@ -267,7 +268,8 @@ let () =
             Some solution, None
         in
         token >>= fun token ->
-        sync_exercise token id ?answer ?editor >>= fun _save ->
+        sync_exercise token id ?answer ?editor (fun () -> Ace.set_synchronized ace)
+        >>= fun _save ->
         select_tab "report" ;
         Lwt_js.yield () >>= fun () ->
         Ace.focus ace ;
@@ -286,7 +288,25 @@ let () =
         Ace.focus ace ;
         typecheck true
   end ;
-  Window.onunload (fun _ev -> local_save ace id; true);
+  (* Small but cross-compatible hack (tested with Firefox-ESR, Chromium, Safari)
+   * that reuses part of this commit:
+   * https://github.com/pfitaxel/learn-ocaml/commit/15780b5b7c91689a26cfeaf33f3ed2cdb3a5e801
+   * For details on this event, see:
+   * https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onbeforeunload#example
+   *
+   * Ideally, we might have wanted to use a variant of [Dom.handler]
+   * that is compatible with "unbeforeunload".
+   * For further discussion on this issue, see:
+   * https://github.com/ocaml-sf/learn-ocaml/issues/467
+   *)
+  let prompt_before_unload () : unit =
+    Js.Unsafe.js_expr "window.onbeforeunload = function(e) {e.preventDefault(); return false;}" in
+  let resume_before_unload () : unit =
+    Js.Unsafe.js_expr "window.onbeforeunload = null" in
+  let () =
+    Ace.register_sync_observer ace (fun sync ->
+        if not sync then prompt_before_unload ()
+        else resume_before_unload ()) in
   (* ---- return -------------------------------------------------------- *)
   toplevel_launch >>= fun _ ->
   typecheck false >>= fun () ->
diff --git a/src/app/learnocaml_index_main.ml b/src/app/learnocaml_index_main.ml
index d3eda82e2..1019e8bf1 100644
--- a/src/app/learnocaml_index_main.ml
+++ b/src/app/learnocaml_index_main.ml
@@ -815,7 +815,7 @@ let () =
           Lwt.return_unit);
       [%i"Sync workspace"], "sync", (fun () ->
           catch_with_alert @@ fun () ->
-          sync () >>= fun _ -> Lwt.return_unit);
+          sync () ignore >>= fun _ -> Lwt.return_unit);
       [%i"Export to file"], "download", download_save;
       [%i"Import"], "upload", import_save;
       [%i"Download all source files"], "download", download_all;
diff --git a/src/app/learnocaml_playground_main.ml b/src/app/learnocaml_playground_main.ml
index d877017b0..fd12cc7e0 100644
--- a/src/app/learnocaml_playground_main.ml
+++ b/src/app/learnocaml_playground_main.ml
@@ -27,8 +27,12 @@ let main () =
   disable_button_group toplevel_buttons_group (* enabled after init *) ;
   let toplevel_toolbar = find_component "learnocaml-exo-toplevel-toolbar" in
   let editor_toolbar = find_component "learnocaml-exo-editor-toolbar" in
-  let toplevel_button =
-    button ~container: toplevel_toolbar ~theme: "dark" ~group:toplevel_buttons_group ?state:None in
+  let toplevel_button ~icon label cb =
+    ignore @@
+      button
+        ~icon ~container: toplevel_toolbar
+        ~theme: "dark" ~group:toplevel_buttons_group ?state:None label cb
+  in
   let id = match Url.Current.path with
     | "" :: "playground" :: p | "playground" :: p ->
         String.concat "/" (List.map Url.urldecode (List.filter ((<>) "") p))
@@ -60,7 +64,7 @@ let main () =
   (* ---- toplevel pane ------------------------------------------------- *)
   init_toplevel_pane toplevel_launch top toplevel_buttons_group toplevel_button ;
   (* ---- editor pane --------------------------------------------------- *)
-  let editor, ace = setup_editor solution in
+  let editor, ace = setup_editor id solution in
   let module EB = Editor_button (struct let ace = ace let buttons_container = editor_toolbar end) in
   EB.cleanup playground.Playground.template;
   EB.download id;
diff --git a/translations/fr.po b/translations/fr.po
index d84b10f73..7aae463af 100644
--- a/translations/fr.po
+++ b/translations/fr.po
@@ -1,4 +1,5 @@
 # LEARN-OCAML FRENCH TRANSLATION
+# Copyright (C) 2020 OCaml Software Foundation.
 # Copyright (C) 2018 OCamlPro
 # Louis Gesbert <louis.gesbert@ocamlpro.com>, 2018.
 #
@@ -99,197 +100,217 @@ msgstr "ERREUR DE REQUÊTE"
 msgid "Could not retrieve data from server"
 msgstr "Échec lors du téléchargement des données du serveur"
 
-#: File "src/app/learnocaml_common.ml", line 414, characters 12-19 454, 11-18
+#: File "src/app/learnocaml_common.ml", line 414, characters 12-19 458, 13-20
 #: "src/app/learnocaml_index_main.ml", 582, 17-24
 msgid "Retry"
 msgstr "Réessayer"
 
-#: File "src/app/learnocaml_common.ml", line 417, characters 25-33 455, 11-19
+#: File "src/app/learnocaml_common.ml", line 417, characters 25-33 459, 13-21
 msgid "Ignore"
 msgstr "Ignorer"
 
-#: File "src/app/learnocaml_common.ml", line 450, characters 26-39
+#: File "src/app/learnocaml_common.ml", line 454, characters 26-39
 msgid "SYNC FAILED"
 msgstr "ECHEC DE LA SYNCHRONISATION"
 
-#: File "src/app/learnocaml_common.ml", line 451, characters 22-66
+#: File "src/app/learnocaml_common.ml", line 455, characters 22-66
 msgid "Could not synchronise save with the server"
 msgstr "Les données n'ont pas pu être synchronisées avec le serveur"
 
-#: File "src/app/learnocaml_common.ml", line 510, characters 39-50
+#: File "src/app/learnocaml_common.ml", line 514, characters 39-50
 msgid "%dd %02dh"
 msgstr "%dj %02dh"
 
-#: File "src/app/learnocaml_common.ml", line 511, characters 40-51
+#: File "src/app/learnocaml_common.ml", line 515, characters 40-51
 msgid "%02d:%02d"
 msgstr "%02d:%02d"
 
-#: File "src/app/learnocaml_common.ml", line 512, characters 23-36
+#: File "src/app/learnocaml_common.ml", line 516, characters 23-36
 msgid "0:%02d:%02d"
 msgstr "0:%02d:%02d"
 
-#: File "src/app/learnocaml_common.ml", line 543, characters 34-55 1071, 38-59
+#: File "src/app/learnocaml_common.ml", line 547, characters 34-55 1147, 38-59
 msgid "difficulty: %d / 40"
 msgstr "difficulté: %d / 40"
 
-#: File "src/app/learnocaml_common.ml", line 578, characters 30-75
+#: File "src/app/learnocaml_common.ml", line 582, characters 30-75
 msgid "No description available for this exercise."
 msgstr "Aucune description pour cet exercice."
 
-#: File "src/app/learnocaml_common.ml", line 601, characters 32-41
+#: File "src/app/learnocaml_common.ml", line 605, characters 32-41
 #: "src/app/learnocaml_index_main.ml", 132, 54-63
 msgid "project"
 msgstr "projet"
 
-#: File "src/app/learnocaml_common.ml", line 602, characters 32-41
+#: File "src/app/learnocaml_common.ml", line 606, characters 32-41
 #: "src/app/learnocaml_index_main.ml", 133, 54-63
 msgid "problem"
 msgstr "problème"
 
-#: File "src/app/learnocaml_common.ml", line 603, characters 33-43
+#: File "src/app/learnocaml_common.ml", line 607, characters 33-43
 #: "src/app/learnocaml_index_main.ml", 134, 55-65
 msgid "exercise"
 msgstr "exercice"
 
-#: File "src/app/learnocaml_common.ml", line 755, characters 26-33
+#: File "src/app/learnocaml_common.ml", line 743, characters 20-39
+msgid "Fetch from server"
+msgstr "Télécharger du serveur"
+
+#: File "src/app/learnocaml_common.ml", line 746, characters 20-43 751,
+msgid "Ignore & keep editing"
+msgstr "Ignorer & continuer d'éditer"
+
+#: File "src/app/learnocaml_common.ml", line 753, characters 20-51
+msgid "Fetch from server & overwrite"
+msgstr "Télécharger du serveur & écraser"
+
+#: File "src/app/learnocaml_common.ml", lines 760-761, characters 28-67
+msgid ""
+"A more recent answer exists on the server. Do you want to fetch the new "
+"version?"
+msgstr ""
+"Une version plus récente de cette réponse existe sur le serveur. Voulez-vous "
+"télécharger la nouvelle version ?"
+
+#: File "src/app/learnocaml_common.ml", line 820, characters 26-33
 msgid "Clear"
 msgstr "Effacer"
 
-#: File "src/app/learnocaml_common.ml", line 760, characters 25-32 881, 24-31
+#: File "src/app/learnocaml_common.ml", line 825, characters 25-32 947, 24-31
 msgid "Reset"
 msgstr "Réinitialiser"
 
-#: File "src/app/learnocaml_common.ml", line 765, characters 22-35
+#: File "src/app/learnocaml_common.ml", line 830, characters 22-35
 msgid "Eval phrase"
 msgstr "Évaluer la phrase"
 
-#: File "src/app/learnocaml_common.ml", line 780, characters 24-51
+#: File "src/app/learnocaml_common.ml", line 845, characters 24-51
 msgid "Preparing the environment"
 msgstr "Préparation de l'environnement"
 
-#: File "src/app/learnocaml_common.ml", line 781, characters 39-47 786, 37-45
+#: File "src/app/learnocaml_common.ml", line 846, characters 39-47 851, 37-45
 msgid "Editor"
 msgstr "Éditeur"
 
-#: File "src/app/learnocaml_common.ml", line 782, characters 41-51
+#: File "src/app/learnocaml_common.ml", line 847, characters 41-51
 #: "src/app/learnocaml_index_main.ml", 691, 30-40
 msgid "Toplevel"
 msgstr "Toplevel"
 
-#: File "src/app/learnocaml_common.ml", line 783, characters 39-47 795,
+#: File "src/app/learnocaml_common.ml", line 848, characters 39-47 860,
 #: "src/app/learnocaml_exercise_main.ml", 58, 30-38 62, 67,
 #: "src/app/learnocaml_student_view.ml", 383, 28-36 396, 400, 405,
 msgid "Report"
 msgstr "Rapport"
 
-#: File "src/app/learnocaml_common.ml", line 784, characters 37-47
+#: File "src/app/learnocaml_common.ml", line 849, characters 37-47
 msgid "Exercise"
 msgstr "Exercice"
 
-#: File "src/app/learnocaml_common.ml", line 785, characters 37-46
+#: File "src/app/learnocaml_common.ml", line 850, characters 37-46
 msgid "Details"
 msgstr "Détails"
 
-#: File "src/app/learnocaml_common.ml", line 787, characters 27-70
+#: File "src/app/learnocaml_common.ml", line 852, characters 27-70
 msgid "Click the Grade button to get your report"
 msgstr "Cliquez sur le bouton Noter pour obtenir votre rapport"
 
-#: File "src/app/learnocaml_common.ml", line 792, characters 22-44
+#: File "src/app/learnocaml_common.ml", line 857, characters 22-44
 msgid "Loading student data"
 msgstr "Chargement des informations sur les étudiants"
 
-#: File "src/app/learnocaml_common.ml", line 793, characters 38-45
+#: File "src/app/learnocaml_common.ml", line 858, characters 38-45
 msgid "Stats"
 msgstr "Statistiques"
 
-#: File "src/app/learnocaml_common.ml", line 794, characters 37-48
+#: File "src/app/learnocaml_common.ml", line 859, characters 37-48
 #: "src/app/learnocaml_index_main.ml", 688, 29-40
 #: "src/app/learnocaml_teacher_tab.ml", 329, 18-29
-#: "src/app/learnocaml_exercise_main.ml", 202, 23-34
+#: "src/app/learnocaml_exercise_main.ml", 203, 23-34
 msgid "Exercises"
 msgstr "Exercices"
 
-#: File "src/app/learnocaml_common.ml", line 796, characters 37-46
+#: File "src/app/learnocaml_common.ml", line 861, characters 37-46
 msgid "Subject"
 msgstr "Énoncé"
 
-#: File "src/app/learnocaml_common.ml", line 797, characters 39-47
+#: File "src/app/learnocaml_common.ml", line 862, characters 39-47
 msgid "Answer"
 msgstr "Réponse"
 
-#: File "src/app/learnocaml_common.ml", line 882, characters 22-42
+#: File "src/app/learnocaml_common.ml", line 948, characters 22-42
 msgid "START FROM SCRATCH"
 msgstr "TOUT RECOMMENCER"
 
-#: File "src/app/learnocaml_common.ml", line 883, characters 16-65
+#: File "src/app/learnocaml_common.ml", line 949, characters 16-65
 msgid "This will discard all your edits. Are you sure?"
 msgstr "Toutes vos modifications seront perdues. Vous êtes sûr·e ?"
 
-#: File "src/app/learnocaml_common.ml", line 890, characters 27-37
+#: File "src/app/learnocaml_common.ml", line 956, characters 27-37
 msgid "Download"
 msgstr "Télécharger"
 
-#: File "src/app/learnocaml_common.ml", line 898, characters 22-33
+#: File "src/app/learnocaml_common.ml", line 964, characters 22-33
 msgid "Eval code"
 msgstr "Exécuter le code"
 
-#: File "src/app/learnocaml_common.ml", line 906, characters 23-29
+#: File "src/app/learnocaml_common.ml", line 974, characters 23-29
 msgid "Sync"
 msgstr "Sync"
 
-#: File "src/app/learnocaml_common.ml", line 964, characters 34-49 999,
+#: File "src/app/learnocaml_common.ml", line 1040, characters 34-49 1075,
 msgid "OCaml prelude"
 msgstr "Prélude OCaml"
 
-#: File "src/app/learnocaml_common.ml", line 971, characters 59-65 1006,
+#: File "src/app/learnocaml_common.ml", line 1047, characters 59-65 1082,
 msgid "Hide"
 msgstr "Cacher"
 
-#: File "src/app/learnocaml_common.ml", line 976, characters 59-65 1013,
+#: File "src/app/learnocaml_common.ml", line 1052, characters 59-65 1089,
 msgid "Show"
 msgstr "Montrer"
 
-#: File "src/app/learnocaml_common.ml", line 1037, characters 18-36
+#: File "src/app/learnocaml_common.ml", line 1113, characters 18-36
 msgid "Enter the secret"
 msgstr "Entrez le secret"
 
-#: File "src/app/learnocaml_common.ml", line 1077, characters 22-35
+#: File "src/app/learnocaml_common.ml", line 1153, characters 22-35
 msgid "Difficulty:"
 msgstr "Difficulté :"
 
-#: File "src/app/learnocaml_common.ml", line 1091, characters 39-49
+#: File "src/app/learnocaml_common.ml", line 1167, characters 39-49
 msgid "Kind: %s"
 msgstr "Type : %s"
 
-#: File "src/app/learnocaml_common.ml", line 1232, characters 46-59
+#: File "src/app/learnocaml_common.ml", line 1308, characters 46-59
 msgid "Identifier:"
 msgstr "Identifiant de l'exercice :"
 
-#: File "src/app/learnocaml_common.ml", line 1236, characters 48-57
+#: File "src/app/learnocaml_common.ml", line 1312, characters 48-57
 msgid "Author:"
 msgstr "Auteur :"
 
-#: File "src/app/learnocaml_common.ml", line 1237, characters 47-57
+#: File "src/app/learnocaml_common.ml", line 1313, characters 47-57
 msgid "Authors:"
 msgstr "Auteurs :"
 
-#: File "src/app/learnocaml_common.ml", line 1242, characters 31-48
+#: File "src/app/learnocaml_common.ml", line 1318, characters 31-48
 msgid "Skills trained:"
 msgstr "Compétences pratiquées :"
 
-#: File "src/app/learnocaml_common.ml", line 1246, characters 31-49
+#: File "src/app/learnocaml_common.ml", line 1322, characters 31-49
 msgid "Skills required:"
 msgstr "Compétences requises :"
 
-#: File "src/app/learnocaml_common.ml", line 1251, characters 36-57
+#: File "src/app/learnocaml_common.ml", line 1327, characters 36-57
 msgid "Previous exercises:"
 msgstr "Exercices précédents :"
 
-#: File "src/app/learnocaml_common.ml", line 1254, characters 35-52
+#: File "src/app/learnocaml_common.ml", line 1330, characters 35-52
 msgid "Next exercises:"
 msgstr "Exercices suivants :"
 
-#: File "src/app/learnocaml_common.ml", line 1259, characters 26-36
+#: File "src/app/learnocaml_common.ml", line 1335, characters 26-36
 msgid "Metadata"
 msgstr "Métadonnées"
 
@@ -517,7 +538,7 @@ msgid "Lessons"
 msgstr "Cours"
 
 #: File "src/app/learnocaml_index_main.ml", line 693, characters 32-44
-#: "src/app/learnocaml_playground_main.ml", 73, 23-35
+#: "src/app/learnocaml_playground_main.ml", 77, 23-35
 msgid "Playground"
 msgstr "Bac-à-sable"
 
@@ -725,45 +746,46 @@ msgstr ""
 "seront plus sauvegardés sur le serveur."
 
 #: File "src/app/learnocaml_exercise_main.ml", line 130, characters 25-49
-#: "src/app/learnocaml_playground_main.ml", 43, 19-43
+#: "src/app/learnocaml_playground_main.ml", 47, 19-43
 msgid "loading the prelude..."
 msgstr "Chargement du prélude..."
 
 #: File "src/app/learnocaml_exercise_main.ml", line 135, characters 41-59
-#: "src/app/learnocaml_playground_main.ml", 46, 31-49
+#: "src/app/learnocaml_playground_main.ml", 50, 31-49
 msgid "error in prelude"
 msgstr "erreur dans le prélude"
 
-#: File "src/app/learnocaml_exercise_main.ml", line 214, characters 28-37
-#: "src/app/learnocaml_playground_main.ml", 80,
+#: File "src/app/learnocaml_exercise_main.ml", line 215, characters 28-37
+#: "src/app/learnocaml_playground_main.ml", 84,
 msgid "Compile"
 msgstr "Compiler"
 
-#: File "src/app/learnocaml_exercise_main.ml", line 218, characters 29-37
+#: File "src/app/learnocaml_exercise_main.ml", line 219, characters 29-37
 msgid "Grade!"
 msgstr "Noter!"
 
-#: File "src/app/learnocaml_exercise_main.ml", line 222, characters 48-55
+#: File "src/app/learnocaml_exercise_main.ml", line 223, characters 48-55
 msgid "abort"
 msgstr "abandonner"
 
-#: File "src/app/learnocaml_exercise_main.ml", lines 226-227, characters 35-65
+#: File "src/app/learnocaml_exercise_main.ml", lines 227-228, characters 35-65
 msgid "Grading is taking a lot of time, maybe your code is looping? "
-msgstr "La notation prend du temps, peut-être une boucle infinie dans votre code ? "
+msgstr ""
+"La notation prend du temps, peut-être une boucle infinie dans votre code ? "
 
-#: File "src/app/learnocaml_exercise_main.ml", line 233, characters 35-57
+#: File "src/app/learnocaml_exercise_main.ml", line 234, characters 35-57
 msgid "Launching the grader"
 msgstr "Lancement de la notation"
 
-#: File "src/app/learnocaml_exercise_main.ml", line 256, characters 60-86
+#: File "src/app/learnocaml_exercise_main.ml", line 257, characters 60-86
 msgid "Grading aborted by user."
 msgstr "Notation annulée par l'utilisateur."
 
-#: File "src/app/learnocaml_exercise_main.ml", line 277, characters 38-59
+#: File "src/app/learnocaml_exercise_main.ml", line 279, characters 38-59
 msgid "Error in your code."
 msgstr "Erreur dans le code."
 
-#: File "src/app/learnocaml_exercise_main.ml", line 278, characters 27-85
+#: File "src/app/learnocaml_exercise_main.ml", line 280, characters 27-85
 msgid "Cannot start the grader if your code does not typecheck."
 msgstr "La notation ne peut être lancée si le code ne compile pas."
 
@@ -893,7 +915,7 @@ msgstr ""
 "%a\n"
 "%!"
 
-#: File "src/grader/grading.ml", line 96, characters 38-65 106, 131, 139,
+#: File "src/grader/grading.ml", line 96, characters 38-65 106, 131, 139, 143,
 msgid "while preparing the tests"
 msgstr "lors de la préparation des tests"
 
@@ -925,15 +947,15 @@ msgstr "lors du chargement de la solution"
 msgid "Preparing to launch the tests."
 msgstr "Préparation du lancement des tests."
 
-#: File "src/grader/grading.ml", line 142, characters 22-49
+#: File "src/grader/grading.ml", line 146, characters 22-49
 msgid "Launching the test bench."
 msgstr "Lancement du banc de test."
 
-#: File "src/grader/grading.ml", line 171, characters 45-78
+#: File "src/grader/grading.ml", line 175, characters 45-78
 msgid "while loading user dependencies"
 msgstr "lors du chargement des dépendances"
 
-#: File "src/grader/grading.ml", line 187, characters 38-67
+#: File "src/grader/grading.ml", line 191, characters 38-67
 msgid "while testing your solution"
 msgstr "lors du test de la solution utilisateur"
 
@@ -945,6 +967,9 @@ msgstr "lors du test de la solution utilisateur"
 #~ "Le téléchargement de l'archive a échoué. Veuillez réessayer "
 #~ "ulterieurement!"
 
+#~ msgid "Do you want to save your work before closing?"
+#~ msgstr "Souhaitez-vous enregistrer votre travail avant de quitter?"
+
 #~ msgid "No description available."
 #~ msgstr "Aucune description."