Index: src/natools-s_expressions-printers.adb
==================================================================
--- src/natools-s_expressions-printers.adb
+++ src/natools-s_expressions-printers.adb
@@ -44,28 +44,32 @@
    end Close_List;
 
 
    procedure Transfer
      (Source : in out Descriptor'Class;
-      Target : in out Printer'Class)
+      Target : in out Printer'Class;
+      Check_Level : in Boolean := False)
    is
       procedure Print_Atom (Data : in Atom);
 
       procedure Print_Atom (Data : in Atom) is
       begin
          Target.Append_Atom (Data);
       end Print_Atom;
 
       Event : Events.Event := Source.Current_Event;
+      Starting_Level : constant Natural := Source.Current_Level;
    begin
       loop
          case Event is
             when Events.Error | Events.End_Of_Input =>
                exit;
             when Events.Open_List =>
                Target.Open_List;
             when Events.Close_List =>
+               exit when Check_Level
+                 and then Source.Current_Level < Starting_Level;
                Target.Close_List;
             when Events.Add_Atom =>
                Source.Query_Atom (Print_Atom'Access);
          end case;
 

Index: src/natools-s_expressions-printers.ads
==================================================================
--- src/natools-s_expressions-printers.ads
+++ src/natools-s_expressions-printers.ads
@@ -39,11 +39,12 @@
    procedure Append_Atom (Output : in out Printer; Data : in Atom) is abstract;
    procedure Close_List (Output : in out Printer) is abstract;
 
    procedure Transfer
      (Source : in out Descriptor'Class;
-      Target : in out Printer'Class);
+      Target : in out Printer'Class;
+      Check_Level : in Boolean := False);
 
    type Canonical (Stream : access Ada.Streams.Root_Stream_Type'Class) is
      new Printer with null record;
 
    overriding procedure Open_List (Output : in out Canonical);