diff --git a/callback.c b/callback.c
index 4720007..b8a2fd5 100644
--- a/callback.c
+++ b/callback.c
@@ -9,43 +9,37 @@
 #include "parsing.h"
 #include "graph_area.h"
 
+/******************************************************************************/
+/*                    W I N D O W S    A C T I V A T I O N                    */
+/******************************************************************************/
+
 static GtkWindow *main_window, *dialog_window;
 
-/******************************************************************************/
-/*                M A I N   W I N D O W   A C T I V A T I O N                 */
-/******************************************************************************/
-void on_main_window_activation (GtkApplication *self, gpointer user_data)
+void on_dialog_window_activation (GtkApplication *app, gpointer no_user_data)
 {
-  main_window = GTK_WINDOW (gtk_application_window_new (self));
-  window_main_child (main_window, 0); //  0 is the state page (see contain.c)
-  window_header_bar (main_window,
-                     "E coli   (with permission from David S. Goodsell, 2009)");
-  gtk_window_present (GTK_WINDOW (main_window));
+  dialog_window = GTK_WINDOW (gtk_application_window_new (app));
+  dialog_window_design (main_window, dialog_window);
 }
 
-void on_dialog_window_activation (GtkApplication *self, gpointer user_data)
+void on_main_window_activation (GtkApplication *app, gpointer no_user_data)
 {
-  dialog_window = GTK_WINDOW (gtk_application_window_new (self));
-  dialog_window_child (dialog_window,0); //  0 is the state page (see contain.c)
-  dialog_window_header_bar (dialog_window, "dialog window");
-//  gtk_window_set_modal (GTK_WINDOW (dialog_window), TRUE);
-  gtk_window_set_transient_for (GTK_WINDOW (dialog_window), GTK_WINDOW (main_window));
-  gtk_window_set_destroy_with_parent (GTK_WINDOW (dialog_window), TRUE);
-  gtk_window_set_deletable (GTK_WINDOW (dialog_window), FALSE); //  FALSE
-  gtk_window_present (GTK_WINDOW (dialog_window));
+  main_window = GTK_WINDOW (gtk_application_window_new (app));
+  main_window_design (main_window);
+  g_signal_connect (app, "activate", G_CALLBACK (on_dialog_window_activation), main_window);
 }
 
+
 void on_auto_notification (const char *message)
 {
   /*  Ignored  (2024-06-06)  because I don't know how to get "main_window" easily
 
     if (window->toast_revealer == NULL) {
-        g_printerr("Can't find self->toast_overlay !\n");
+        g_printerr("Can't find app->toast_overlay !\n");
         return;
     }
 
     if (window->toast_text == NULL) {
-        g_printerr("Can't find self->toast_overlay !\n");
+        g_printerr("Can't find app->toast_overlay !\n");
         return;
     }
 
diff --git a/callback.h b/callback.h
index f6c2a43..47185f2 100644
--- a/callback.h
+++ b/callback.h
@@ -2,7 +2,7 @@
 
 
 void on_main_window_activation (GtkApplication *app, gpointer user_data);
-void on_dialog_window_activation (GtkApplication *self, gpointer user_data);
+void on_dialog_window_activation (GtkApplication *app, gpointer user_data);
 void on_auto_notification (const char *message);
 
 void on_user_tree_expander_toggled (GtkExpander *expander, gpointer user_data);
diff --git a/contain.c b/contain.c
index db53237..3710dfc 100644
--- a/contain.c
+++ b/contain.c
@@ -209,6 +209,12 @@ void window_main_child (GtkWindow *main_window, int selected_page){
   }
 }
 
+void main_window_design (GtkWindow *main_window){
+  window_main_child (main_window, 0); //  0 is the state page
+  window_header_bar (main_window,
+                     "E coli   (with permission from David S. Goodsell, 2009)");
+  gtk_window_present (GTK_WINDOW (main_window));
+}
 
 
 
diff --git a/contain.h b/contain.h
index 91f5419..93ab316 100644
--- a/contain.h
+++ b/contain.h
@@ -30,8 +30,7 @@ MyApplication *my_application_new (const char *application_id, GApplicationFlags
 G_END_DECLS
 */
 
-void window_header_bar (GtkWindow *window, char *title);
-void window_main_child (GtkWindow *window, int selected_page);
+void main_window_design (GtkWindow *main_window);
 void two_notebooks_in_two_panes (GtkWindow *window);
 GtkWidget *get_selected_rules_vpaned_new();
 GtkFrame *get_frame_with_label();
diff --git a/dialog.c b/dialog.c
index 3c876d7..3687a05 100644
--- a/dialog.c
+++ b/dialog.c
@@ -9,11 +9,25 @@
 
 // https://docs.gtk.org/gtk4/visual_index.html  <  widgets gallery
 
+/*  doc : see  >  on_dialog_window_activation (...)  in  callback.c   */
 
-void dialog_window_child (GtkWindow *dialog_window, int selected_page){}
-
-void dialog_window_header_bar (GtkWindow *dialog_window, char *title){
+void dialog_window_design (GtkWindow *main_window, GtkWindow *dialog_window){
+  char *title =  "     Should I save  the  current  model  before  editing  ?     ";
   GtkWidget *header_bar = GTK_WIDGET (gtk_header_bar_new ());
   gtk_header_bar_set_title_widget (GTK_HEADER_BAR (header_bar), gtk_label_new (title));
   gtk_window_set_titlebar (dialog_window, header_bar);
+
+  GtkBox *page_box = GTK_BOX (gtk_box_new (GTK_ORIENTATION_VERTICAL, 2));
+  GtkButton *click = GTK_BUTTON (gtk_button_new_with_label ("click me !"));
+  gtk_box_append (page_box, GTK_WIDGET (click));
+  //  gtk_box_append (page_box, GTK_WIDGET (gtk_separator_new (GTK_ORIENTATION_HORIZONTAL)));
+  gtk_window_set_child (dialog_window, GTK_WIDGET (page_box));
+
+  gtk_window_set_transient_for (GTK_WINDOW (dialog_window), GTK_WINDOW (main_window));
+  gtk_window_set_destroy_with_parent (GTK_WINDOW (dialog_window), TRUE);
+  //  gtk_window_set_deletable (GTK_WINDOW (dialog_window), FALSE); //  FALSE
+  //  gtk_window_set_modal (GTK_WINDOW (dialog_window), TRUE);
+  gtk_window_present (GTK_WINDOW (dialog_window));
 }
+
+
diff --git a/dialog.h b/dialog.h
index 9d8a58e..ab07aba 100644
--- a/dialog.h
+++ b/dialog.h
@@ -1,5 +1,4 @@
 #include <gtk-4.0/gtk/gtk.h>
 
-void dialog_window_header_bar (GtkWindow *dialog_window, char *title);
-void dialog_window_child (GtkWindow *dialog_window, int selected_page);
+void dialog_window_design (GtkWindow *main_window, GtkWindow *dialog_window);