diff --git a/src/lib/diff/diff.cpp b/src/lib/diff/diff.cpp
index af7be6ee3..2790fc03e 100644
--- a/src/lib/diff/diff.cpp
+++ b/src/lib/diff/diff.cpp
@@ -32,8 +32,10 @@
 
 
 #include "lib/error.hpp"
+#include "lib/format-util.hpp"
 #include "lib/diff/diff-language.hpp"
 #include "lib/diff/gen-node.hpp"
+#include "lib/variant.hpp"
 
 
 namespace lib {
@@ -49,9 +51,18 @@ namespace diff{
   Ref Ref::THIS   ("_THIS_");
   Ref Ref::CHILD  ("_CHILD_");
   Ref Ref::ATTRIBS("_ATTRIBS_");
-
   
-  /** Implementation of content equality test */
+  
+  
+  
+  /** Implementation of content equality test
+   * @throws error::Logic when the given other DataCap
+   *         does not hold a value of the same type than
+   *         this DataCap.
+   * @remarks since the GenNode::ID is generated including a type hash,
+   *         the equality operator of GenNode ensures this content test
+   *         is only called on a compatible DataCap.
+   */
   bool
   DataCap::operator== (DataCap const& o)  const
   {
@@ -92,5 +103,11 @@ namespace diff{
     unConst(this)->accept(visitor);
     return visitor;
   }
-
+  
+  DataCap::operator string()  const
+  {
+    return "DataCap|"+string(this->buffer());
+  }
+  
+  
 }} // namespace lib::diff
diff --git a/src/lib/diff/gen-node.hpp b/src/lib/diff/gen-node.hpp
index 2279ba5cb..79218166c 100644
--- a/src/lib/diff/gen-node.hpp
+++ b/src/lib/diff/gen-node.hpp
@@ -95,20 +95,18 @@
 #define LIB_DIFF_GEN_NODE_H
 
 
-#include "lib/hash-indexed.hpp"                 ///< @warning needs to be first, see explanation in lib/hash-standard.hpp
-
 #include "lib/error.hpp"
-#include "lib/variant.hpp"
-#include "lib/time/timevalue.hpp"
-#include "lib/diff/record.hpp"
 #include "lib/idi/entry-id.hpp"
+#include "lib/time/timevalue.hpp"
 //#include "lib/util.hpp"
 //#include "lib/format-string.hpp"
 //#include "lib/format-util.hpp"
+#include "lib/diff/record.hpp"
 #include "lib/variant.hpp"
 #include "lib/util.hpp"
 
 //#include <vector>
+#include <utility>
 #include <string>
 //#include <map>
 
@@ -178,6 +176,7 @@ namespace diff{
       DataCap& operator= (DataCap&&)       =default;
       
       bool operator== (DataCap const&)  const;
+      operator string()  const;
     };
   
   
@@ -247,6 +246,12 @@ namespace diff{
       
       
       
+      /** @internal diagnostics helper. Need to include format-helper.cpp */
+      operator string()  const
+        {
+          return "GenNode-"+string(idi)+"-"+string(data);
+        }
+      
       bool
       isNamed()  const
         {
@@ -405,7 +410,7 @@ namespace diff{
   inline string
   Rec::renderAttribute (GenNode const& a)
   {
-    return a.idi.getSym() +" = "+string(a.data);
+    return a.idi.getSym() +" = "+ string(a.data);
   }
   
   template<>
diff --git a/src/lib/format-util.hpp b/src/lib/format-util.hpp
index dc7ef0e5a..ef472797d 100644
--- a/src/lib/format-util.hpp
+++ b/src/lib/format-util.hpp
@@ -37,6 +37,7 @@
 #ifndef LIB_FORMAT_UTIL_H
 #define LIB_FORMAT_UTIL_H
 
+#include "lib/hash-standard.hpp"
 #include "lib/meta/trait.hpp"
 #include "lib/itertools.hpp"
 #include "lib/symbol.hpp"
@@ -209,4 +210,4 @@ namespace util {
   
   
 } // namespace util
-#endif
+#endif /*LIB_FORMAT_UTIL_H*/
diff --git a/src/lib/hash-indexed.hpp b/src/lib/hash-indexed.hpp
index 7069d296f..325b2c706 100644
--- a/src/lib/hash-indexed.hpp
+++ b/src/lib/hash-indexed.hpp
@@ -56,6 +56,7 @@
 
 #include "lib/hash-value.h"
 #include "lib/hash-standard.hpp"
+#include "lib/error.hpp"
 
 extern "C" {
 #include "lib/luid.h"
diff --git a/src/lib/meta/virtual-copy-support.hpp b/src/lib/meta/virtual-copy-support.hpp
index 0e502f579..0fea250de 100644
--- a/src/lib/meta/virtual-copy-support.hpp
+++ b/src/lib/meta/virtual-copy-support.hpp
@@ -126,7 +126,6 @@ namespace lib {
 namespace meta{
   
   using std::move;
-  using util::unConst;
   
   using std::is_move_constructible;
   using std::is_copy_constructible;
diff --git a/src/lib/variant.hpp b/src/lib/variant.hpp
index 9902e1746..c5fb04477 100644
--- a/src/lib/variant.hpp
+++ b/src/lib/variant.hpp
@@ -78,10 +78,12 @@
 #define LIB_VARIANT_H
 
 
+#include "lib/error.hpp"
 #include "lib/meta/typelist.hpp"
 #include "lib/meta/typelist-util.hpp"
 #include "lib/meta/generator.hpp"
 #include "lib/meta/virtual-copy-support.hpp"
+#include "lib/util.hpp"
 
 #include <type_traits>
 #include <utility>
@@ -434,16 +436,17 @@ namespace lib {
   template<typename TYPES>
   Variant<TYPES>::operator string()  const
   {
-    return string(buffer());
+    return "Variant|" + string(buffer());
   }
   
   template<typename TYPES>
   template<typename TY>
   Variant<TYPES>::Buff<TY>::operator string()  const
   {
-    return "Variant|"
-#ifdef LIB_FORMAT_UTIL_H
-        +  util::str (this->access(),
+#ifndef LIB_FORMAT_UTIL_H
+    return string("-?-")+typeid(TY).name()+"-?-";
+#else
+    return util::str (this->access(),
                      (util::tyStr<TY>()+"|").c_str())
 #endif
                      ;
diff --git a/tests/library/diff/gen-node-basic-test.cpp b/tests/library/diff/gen-node-basic-test.cpp
index 6fe4e4ca3..8d0ff2f0d 100644
--- a/tests/library/diff/gen-node-basic-test.cpp
+++ b/tests/library/diff/gen-node-basic-test.cpp
@@ -23,6 +23,7 @@
 
 #include "lib/test/run.hpp"
 #include "lib/test/test-helper.hpp"
+#include "lib/format-util.hpp"
 #include "lib/diff/gen-node.hpp"
 #include "lib/diff/record.hpp"
 #include "lib/time/timevalue.hpp"
@@ -31,6 +32,7 @@
 //#include <utility>
 //#include <string>
 //#include <vector>
+#include <iostream>
 #include <cmath>
 
 using util::isnil;
@@ -44,6 +46,8 @@ using lib::time::TimeSpan;
 //using std::vector;
 //using std::swap;
 using std::fabs;
+using std::cout;
+using std::endl;
 
 
 namespace lib {
@@ -143,6 +147,8 @@ namespace test{
           CHECK ("ham"  == n3.data.get<Rec>().get("ham").idi.getSym());
           CHECK (n3.data.get<Rec>().get("ham").isNamed());
           CHECK (!n3.isNamed());
+          
+          cout << string(n3) <<endl; // diagnostic spam
         }
       
       
diff --git a/tests/library/diff/generic-tree-mutator-test.cpp b/tests/library/diff/generic-tree-mutator-test.cpp
index f6b10803e..149783211 100644
--- a/tests/library/diff/generic-tree-mutator-test.cpp
+++ b/tests/library/diff/generic-tree-mutator-test.cpp
@@ -22,6 +22,7 @@
 
 
 #include "lib/test/run.hpp"
+#include "lib/format-util.hpp"
 #include "lib/test/test-helper.hpp"
 #include "lib/diff/tree-mutator.hpp"
 #include "lib/util.hpp"