diff --git a/src/lib/diff/gen-node.hpp b/src/lib/diff/gen-node.hpp
index 35de92db4..95c90c6bd 100644
--- a/src/lib/diff/gen-node.hpp
+++ b/src/lib/diff/gen-node.hpp
@@ -118,6 +118,7 @@ namespace diff{
   using std::string;
   
   struct GenNode;
+  struct Ref;
   
   /** Define actual data storage and access types used */
   template<>
@@ -253,9 +254,10 @@ namespace diff{
                                        ////////////////////////TICKET #963  Forwarding shadows copy operations -- generic solution??
       GenNode(GenNode const&)  =default;
       GenNode(GenNode&&)       =default;
-      GenNode(GenNode& o)
-        : GenNode((GenNode const&)o)
-        { }
+      GenNode(GenNode& o)    : GenNode((GenNode const&)o) { }
+      GenNode(Ref const& r)  : GenNode((GenNode const&)r) { }
+      GenNode(Ref &  r)      : GenNode((GenNode const&)r) { }
+      GenNode(Ref && r)      : GenNode((GenNode &&)r)     { }
       
       GenNode& operator= (GenNode const&)  =default;
       GenNode& operator= (GenNode&&)       =default;
diff --git a/src/lib/diff/tree-diff-application.hpp b/src/lib/diff/tree-diff-application.hpp
index 0ab0ac5eb..16b58620b 100644
--- a/src/lib/diff/tree-diff-application.hpp
+++ b/src/lib/diff/tree-diff-application.hpp
@@ -55,6 +55,68 @@ namespace diff{
     : public TreeDiffInterpreter
     {
       
+      
+      /* == Implementation of the list diff application primitives == */
+      
+      void
+      ins (GenNode n)  override
+        {
+          UNIMPLEMENTED("insert node");
+        }
+      
+      void
+      del (GenNode n)  override
+        {
+          UNIMPLEMENTED("delete next node");
+        }
+      
+      void
+      pick (GenNode n)  override
+        {
+          UNIMPLEMENTED("accept next node as-is");
+        }
+      
+      void
+      skip (GenNode n)  override
+        {
+          UNIMPLEMENTED("skip void position left by find");
+        }      // assume the actual content has been moved away by a previous find()
+      
+      void
+      find (GenNode n)  override
+        {
+          UNIMPLEMENTED("search the named node and insert it here");
+        }      // consume and leave waste, expected to be cleaned-up by skip() later
+      
+      
+      
+      /* == Implementation of the tree diff application primitives == */
+      
+      void
+      after (GenNode n)  override
+        {
+          UNIMPLEMENTED("cue to a position behind the named node");
+        }
+      
+      void
+      mut (GenNode n)  override
+        {
+          UNIMPLEMENTED("open nested context for diff");
+        }
+      
+      void
+      emu (GenNode n)  override
+        {
+          UNIMPLEMENTED("finish and leave nested diff context");
+        }
+      
+      
+    public:
+      explicit
+      DiffApplicationStrategy(Rec& targetRecord)
+        {
+          UNIMPLEMENTED();
+        }
     };
   
   
diff --git a/src/lib/diff/tree-diff.hpp b/src/lib/diff/tree-diff.hpp
index a3c8f1dd0..550ff26bc 100644
--- a/src/lib/diff/tree-diff.hpp
+++ b/src/lib/diff/tree-diff.hpp
@@ -42,6 +42,7 @@
 
 
 #include "lib/diff/diff-language.hpp"
+#include "lib/diff/list-diff.hpp"
 #include "lib/diff/gen-node.hpp"
 
 
@@ -60,11 +61,38 @@ namespace diff{
   class TreeDiffInterpreter
     {
     public:
+      using Val = GenNode;
       
-      ///////TODO actual operations go here
+      virtual ~TreeDiffInterpreter() { } ///< this is an interface
+      
+      virtual void ins (GenNode n)   =0;
+      virtual void del (GenNode n)   =0;
+      virtual void pick(GenNode n)   =0;
+      virtual void find(GenNode n)   =0;
+      virtual void skip(GenNode n)   =0;
+      
+      virtual void after(GenNode n)  =0;
+      virtual void mut (GenNode n)   =0;
+      virtual void emu (GenNode n)   =0;
     };
   
-  using TreeDiffLanguage = DiffLanguage<TreeDiffInterpreter, GenNode>;
+  struct TreeDiffLanguage
+    : DiffLanguage<TreeDiffInterpreter, GenNode>
+    {
+      using Interpreter = TreeDiffInterpreter;
+      
+      // List Diff sub language
+      DiffStep_CTOR(ins);
+      DiffStep_CTOR(del);
+      DiffStep_CTOR(pick);
+      DiffStep_CTOR(find);
+      DiffStep_CTOR(skip);
+      
+      // Tree structure verbs
+      DiffStep_CTOR(after);
+      DiffStep_CTOR(mut);
+      DiffStep_CTOR(emu);
+    };
   
   
   
diff --git a/tests/library/diff/diff-tree-application-test.cpp b/tests/library/diff/diff-tree-application-test.cpp
index 68e95255a..ba6488699 100644
--- a/tests/library/diff/diff-tree-application-test.cpp
+++ b/tests/library/diff/diff-tree-application-test.cpp
@@ -68,6 +68,8 @@ namespace test{
     DiffStep_CTOR(pick);
     DiffStep_CTOR(find);
     DiffStep_CTOR(skip);
+    
+    DiffStep_CTOR(after);
     DiffStep_CTOR(mut);
     DiffStep_CTOR(emu);