diff --git a/src/lib/iter-tree-explorer.hpp b/src/lib/iter-tree-explorer.hpp
index b7e539279..dfdfac94a 100644
--- a/src/lib/iter-tree-explorer.hpp
+++ b/src/lib/iter-tree-explorer.hpp
@@ -268,7 +268,7 @@ namespace lib {
     struct _TreeExplorerTraits<SRC,   enable_if<is_StateCore<SRC>>>
       {
         using SrcVal  = typename std::remove_reference<decltype(yield (std::declval<SRC>()))>::type;
-        using SrcIter = IterStateWrapper<SrcVal, SRC>;
+        using SrcIter = iter_source::IterableDecorator<SrcVal, SRC>;
       };
     
     template<class SRC>
@@ -290,7 +290,7 @@ namespace lib {
     struct ArgAccessor
       {
         using FunArg = typename _Fun<SIG>::Args::List::Head;
-        static_assert (std::is_convertible<FunArg, ARG>::value,
+        static_assert (std::is_convertible<ARG, FunArg>::value,
                        "the expansion functor must accept the source iterator or state core as parameter");
 
         static auto accessor() { return [](auto arg) { return arg; }; }
diff --git a/tests/library/iter-tree-explorer-test.cpp b/tests/library/iter-tree-explorer-test.cpp
index a34c0ba88..39692241f 100644
--- a/tests/library/iter-tree-explorer-test.cpp
+++ b/tests/library/iter-tree-explorer-test.cpp
@@ -302,10 +302,22 @@ namespace test{
       void
       verify_expandOperation()
         {
-          auto ii = treeExplore(CountDown{5})
+          verify_treeExpandingIterator(
+                    treeExplore(CountDown{5})
                       .expand([](uint j){ return CountDown{j-1}; })
-                      ;
+                      );
           
+          verify_treeExpandingIterator(
+                    treeExplore(CountDown{5})
+                      .expand([](CountDown const& core){ return CountDown{ yield(core) - 1}; })
+                      );
+        }
+      
+      
+      template<class EXP>
+      void
+      verify_treeExpandingIterator(EXP ii)
+        {
           CHECK (!isnil (ii));
           CHECK (5 == *ii);
           ++ii;
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 03d0b51a8..504819676 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -5131,8 +5131,8 @@
 <node CREATED="1511227821087" ID="ID_1644135845" MODIFIED="1511227823932" TEXT="monadisch"/>
 <node CREATED="1511227824495" ID="ID_1299746114" MODIFIED="1511227836441" TEXT="Val -&gt; Iter(Val)"/>
 </node>
-<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511227861867" ID="ID_1821706302" MODIFIED="1511228200056" TEXT="Fall-2 ">
-<icon BUILTIN="flag-yellow"/>
+<node COLOR="#338800" CREATED="1511227861867" ID="ID_1821706302" MODIFIED="1511404000144" TEXT="Fall-2 ">
+<icon BUILTIN="button_ok"/>
 <node CREATED="1511227870346" ID="ID_797579225" MODIFIED="1511228200055" TEXT="verzahnte Implementierung"/>
 <node CREATED="1511227975028" ID="ID_1769405758" MODIFIED="1511228200056" TEXT="Sub-F&#xe4;lle">
 <node CREATED="1511227902005" ID="ID_1992381343" MODIFIED="1511228200056" TEXT="Core -&gt; Iter(Val)"/>
@@ -5168,8 +5168,8 @@
 </node>
 </node>
 </node>
-<node BACKGROUND_COLOR="#fdfdcf" COLOR="#ff0000" CREATED="1511228184223" ID="ID_1701796180" MODIFIED="1511228192928" TEXT="Vereinigung">
-<icon BUILTIN="flag-pink"/>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1511228184223" HGAP="26" ID="ID_1701796180" MODIFIED="1511404034527" TEXT="Vereinigung" VSHIFT="23">
+<icon BUILTIN="messagebox_warning"/>
 <node CREATED="1511228210268" ID="ID_268486334" MODIFIED="1511228224230" TEXT="im Fall-1 m&#xfc;ssen wir operator* anwenden"/>
 <node CREATED="1511228226946" ID="ID_1853550246" MODIFIED="1511228237684" TEXT="im Fall-2 m&#xfc;ssen wir einen Core-Typ konstruieren">
 <node CREATED="1511228291778" ID="ID_1396258052" MODIFIED="1511228302748" TEXT="und zwar einen, den die Funktion nehmen kann"/>
@@ -5177,9 +5177,17 @@
 <icon BUILTIN="messagebox_warning"/>
 </node>
 </node>
-<node BACKGROUND_COLOR="#fdfdcf" COLOR="#ff0000" CREATED="1511228361960" ID="ID_757059750" MODIFIED="1511228379781" TEXT="wie bringt man das syntaktisch auf eine einzige Linie??">
+<node CREATED="1511228361960" ID="ID_757059750" MODIFIED="1511402807191" TEXT="wie bringt man das syntaktisch auf eine einzige Linie??">
+<font ITALIC="true" NAME="SansSerif" SIZE="12"/>
 <icon BUILTIN="help"/>
 </node>
+<node CREATED="1511402785895" ID="ID_1409331699" MODIFIED="1511402797347" TEXT="L&#xf6;sungsidee: generisches Lambda">
+<icon BUILTIN="idea"/>
+<node CREATED="1511402832809" ID="ID_844588469" MODIFIED="1511402843611" TEXT="wird einmal auf der initialen Quelle aufgerufen"/>
+<node CREATED="1511402844151" ID="ID_504070749" MODIFIED="1511402854442" TEXT="oder dann auf einem der Sub-Iteratoren auf dem Stack"/>
+<node CREATED="1511402855174" ID="ID_386377958" MODIFIED="1511402861001" TEXT="beides k&#xf6;nnen unterschiedliche Typen sein"/>
+<node CREATED="1511402861613" ID="ID_1536434222" MODIFIED="1511402872072" TEXT="solange der expandFunktor beide akzeptiert...."/>
+</node>
 </node>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1510969031379" ID="ID_358406634" MODIFIED="1511227807158" TEXT="verify_transformOperation();">