diff --git a/src/proc/mobject/placement-ref.hpp b/src/proc/mobject/placement-ref.hpp
index c70e4cf1e..37f629472 100644
--- a/src/proc/mobject/placement-ref.hpp
+++ b/src/proc/mobject/placement-ref.hpp
@@ -167,7 +167,7 @@ namespace mobject {
       bool operator!= (PlacementRef<O> const& o)  const { return id_ != o; }
       
       
-      typedef _Id PlacementRef::*__unspecified_bool_type;
+      typedef _Id PlacementRef::*__unspecified_bool_type; ////////TICKET #178 :  implement by lib::BoolCheckable?
       
       /** implicit conversion to "bool" */ 
       operator __unspecified_bool_type()  const { return  isValid()? &PlacementRef::id_ : 0; }  // never throws
diff --git a/src/proc/mobject/session/scope.cpp b/src/proc/mobject/session/scope.cpp
index fe5f60bcb..6c00a222e 100644
--- a/src/proc/mobject/session/scope.cpp
+++ b/src/proc/mobject/session/scope.cpp
@@ -50,6 +50,44 @@ namespace session {
   
   
   
+  /** discover the enclosing scope of a given Placement */
+  Scope const&
+  Scope::containing (PlacementMO const& aPlacement)
+  {
+    UNIMPLEMENTED ("scope discovery");
+  }
+  
+  
+  /** retrieve the parent scope which encloses this scope.
+   *  @throw error::Invalid if this is the root scope
+   */
+  Scope const&
+  Scope::getParent()  const
+  {
+    UNIMPLEMENTED ("retrieve the enclosing parent scope");
+  }
+  
+  
+  /** @return true if this is the outmost (root) scope */
+  bool
+  Scope::isRoot()  const
+  {
+    UNIMPLEMENTED ("detection of root scope");
+  }
+  
+  
+  /** enumerate the path of nested scopes up to root scope.
+   *  @return an iterator which starts with this scope and
+   *          successively yields outer scopes, stopping at root.
+   */
+  Scope::IterType_
+  Scope::ascend()  const
+  {
+    UNIMPLEMENTED ("ascend scope hierarchy up to root");
+  }
+
+  
+  
   
   
   
diff --git a/src/proc/mobject/session/scope.hpp b/src/proc/mobject/session/scope.hpp
index fa7a0a0a7..c4bffae06 100644
--- a/src/proc/mobject/session/scope.hpp
+++ b/src/proc/mobject/session/scope.hpp
@@ -28,6 +28,7 @@
 //#include "proc/mobject/mobject.hpp"
 #include "proc/mobject/placement.hpp"
 #include "proc/mobject/placement-ref.hpp"
+#include "lib/iter-adapter.hpp"
 #include "lib/singleton.hpp"
 
 #include <boost/scoped_ptr.hpp>
@@ -41,6 +42,7 @@ namespace mobject {
 namespace session {
   
   using boost::scoped_ptr;
+  using lib::IterAdapter;
   
   class ScopeLocator;
   class QueryFocusStack;
@@ -53,6 +55,8 @@ namespace session {
     {
       RefPlacement anchor_;
       
+      typedef IterAdapter<PlacementMO*, Scope> IterType_;
+      
     public:
       Scope (PlacementMO const& constitutingPlacement);
       
@@ -60,6 +64,11 @@ namespace session {
       static Scope const& containing (RefPlacement const& refPlacement);
       
       Scope const& getParent()  const;
+      PlacementMO& getTop()  const;
+      bool isRoot()  const;
+      
+      typedef IterType_ iterator;
+      iterator ascend()  const;
     };
   
   
@@ -74,5 +83,21 @@ namespace session {
 ///////////////////////////TODO currently just fleshing the API
   
   
+  
+  inline Scope const&
+  Scope::containing (RefPlacement const& refPlacement)
+  {
+    return containing (*refPlacement);
+  }
+  
+  
+  inline PlacementMO&
+  Scope::getTop()  const
+  {
+    ASSERT (anchor_);
+    return *anchor_;
+  }
+  
+  
 }} // namespace mobject::session
 #endif
diff --git a/tests/components/proc/mobject/placement-scope-test.cpp b/tests/components/proc/mobject/placement-scope-test.cpp
index f89cc4f4d..cac6cc14b 100644
--- a/tests/components/proc/mobject/placement-scope-test.cpp
+++ b/tests/components/proc/mobject/placement-scope-test.cpp
@@ -47,12 +47,13 @@ namespace test    {
   
 //  using namespace mobject::test;
 //  typedef TestPlacement<TestSubMO21> PSub;
+  using lumiera::error::LUMIERA_ERROR_INVALID;
   
   
   /***************************************************************************
    * @test basic behaviour of the nested placement search scopes.
-   *       Using a pseudo-session (actually just a PlacementIndex), this test
-   *       creates some nested scopes and then...
+   *       Using a pseudo-session (actually just a PlacementIndex),
+   *       this test creates some nested scopes and then...
    *       - discovers the scope of a placement
    *       - finds the parent scope
    *       - enumerates a scope path up to root