diff --git a/src/multi_array_operation.h b/src/multi_array_operation.h
index b875a63..5bdbf44 100644
--- a/src/multi_array_operation.h
+++ b/src/multi_array_operation.h
@@ -31,7 +31,7 @@ namespace MultiArrayTools
     template <typename T>
     struct plus
     {
-	static T&& apply(T&& a1, T&& a2)
+	static T apply(const T& a1, const T& a2)
 	{
 	    return a1 + a2;
 	}
@@ -40,7 +40,7 @@ namespace MultiArrayTools
     template <typename T>
     struct minus
     {
-	static T&& apply(T&& a1, T&& a2)
+	static T apply(const T& a1, const T& a2)
 	{
 	    return a1 - a2;
 	}
@@ -49,7 +49,7 @@ namespace MultiArrayTools
     template <typename T>
     struct multiplies
     {
-	static T&& apply(T&& a1, T&& a2)
+	static T apply(const T& a1, const T& a2)
 	{
 	    return a1 * a2;
 	}
@@ -58,7 +58,7 @@ namespace MultiArrayTools
     template <typename T>
     struct divides
     {
-	static T&& apply(T&& a1, T&& a2)
+	static T apply(const T& a1, const T& a2)
 	{
 	    return a1 / a2;
 	}
@@ -350,7 +350,7 @@ namespace MultiArrayTools
 	const BlockResult<T>& get() const;
 	
 	template <class ET, size_t SITE>
-	inline T&& get(const ET& pos) const;
+	inline T get(const ET& pos) const;
 
 	std::vector<BTSS> block(const IndexInfo* blockIndex, bool init = false) const;
 	const Operation& block() const;
@@ -390,7 +390,7 @@ namespace MultiArrayTools
 	const BlockResult<T>& get() const;
 
 	template <class ET, size_t SITE>
-	inline T&& get(const ET& pos) const;
+	inline T get(const ET& pos) const;
 
 	std::vector<BTSS> block(const IndexInfo* blockIndex, bool init = false) const;
 	const Contraction& block() const;
@@ -527,7 +527,7 @@ namespace MultiArrayTools
     inline void OperationMaster<T,OpClass,Ranges...>::AssignmentExpr::
     operator()(size_t start, const ETuple& last)
     {
-	mM.get(start) = mSec.template get<ETuple,OpClass::SIZE>(last);
+	mM.get(start) = mSec.template get<ETuple,OpClass::SIZE-1>(last);
     }
     
     template <typename T, class OpClass, class... Ranges>
@@ -622,12 +622,14 @@ namespace MultiArrayTools
     template <typename T, class OpClass, class... Ranges>
     T& OperationMaster<T,OpClass,Ranges...>::get(size_t pos)
     {
+	VCHECK(pos);
 	return mData[pos];
     }
 
     template <typename T, class OpClass, class... Ranges>
     const T& OperationMaster<T,OpClass,Ranges...>::get(size_t pos) const
     {
+	VCHECK(pos);
 	return mData[pos];
     }
     
@@ -840,11 +842,11 @@ namespace MultiArrayTools
 
     template <typename T, class OpFunction, class... Ops>
     template <class ET, size_t SITE>
-    inline T&& Operation<T,OpFunction,Ops...>::get(const ET& pos) const
+    inline T Operation<T,OpFunction,Ops...>::get(const ET& pos) const
     {
 	typedef std::tuple<Ops const&...> OpTuple;
-	return std::forward<T>( PackNum<sizeof...(Ops)-2>::
-				template mkOpExpr<T,ET,OpTuple,OpFunction,SITE>(pos, mOps) );
+	return PackNum<sizeof...(Ops)-2>::
+	    template mkOpExpr<T,ET,OpTuple,OpFunction,SITE>(pos, mOps);
     }
     
     template <typename T, class OpFunction, class... Ops>
@@ -908,9 +910,9 @@ namespace MultiArrayTools
     // forward loop !!!!
     template <typename T, class Op, class IndexType>
     template <class ET, size_t SITE>
-    inline T&& Contraction<T,Op,IndexType>::get(const ET& pos) const
+    inline T Contraction<T,Op,IndexType>::get(const ET& pos) const
     {
-	return std::forward<T>( mOp.template get<SITE>(pos) );
+	return mOp.template get<ET,SITE>(pos);
     }
 
     template <typename T, class Op, class IndexType>
diff --git a/src/pack_num.h b/src/pack_num.h
index 4e585f3..e0cc991 100644
--- a/src/pack_num.h
+++ b/src/pack_num.h
@@ -68,12 +68,13 @@ namespace MultiArrayHelper
 
 	// call with -2 (instead of -1)
 	template <typename T, class ETuple, class OpTuple, class OpFunction, size_t START>
-	static T&& mkOpExpr(const ETuple& pos, const OpTuple& ops)
+	static T mkOpExpr(const ETuple& pos, const OpTuple& ops)
 	{
-	    static const size_t NEXT = START - std::tuple_element<N+1,OpTuple>::type::SIZE;
-	    return std::forward<T>
-		( OpFunction::apply( std::get<N+1>(ops).template get<START>(pos),
-				     PackNum<N-1>::template mkOpExpr<ETuple,OpTuple,OpFunction,NEXT>(pos, ops) ) );
+	    typedef typename std::tuple_element<N,OpTuple>::type SubOpTypeRef;
+	    typedef typename std::remove_reference<SubOpTypeRef>::type SubOpType;
+	    static const size_t NEXT = START - SubOpType::SIZE;
+	    return  OpFunction::apply( std::get<N+1>(ops).template get<ETuple,START>(pos),
+				       PackNum<N-1>::template mkOpExpr<ETuple,OpTuple,OpFunction,NEXT>(pos, ops) );
 	}
 
 	template <class OpTuple, class Expr>
@@ -137,12 +138,13 @@ namespace MultiArrayHelper
 	}
 
 	template <typename T, class ETuple, class OpTuple, class OpFunction, size_t START>
-	static T&& mkOpExpr(const ETuple& pos, const OpTuple& ops)
+	static T mkOpExpr(const ETuple& pos, const OpTuple& ops)
 	{
-	    static const size_t NEXT = START - std::tuple_element<1,OpTuple>::type::SIZE;
-	    return std::forward<T>
-		( OpFunction::apply( std::get<1>(ops).template get<START>(pos),
-				     std::get<0>(ops).template get<NEXT>(pos) ) );
+	    typedef typename std::tuple_element<1,OpTuple>::type SubOpTypeRef;
+	    typedef typename std::remove_reference<SubOpTypeRef>::type SubOpType;
+	    static const size_t NEXT = START - SubOpType::SIZE;
+	    return OpFunction::apply( std::get<1>(ops).template get<ETuple,START>(pos),
+				      std::get<0>(ops).template get<ETuple,NEXT>(pos) );
 	}
 
 	template <class OpTuple, class Expr>
diff --git a/src/ranges/container_range.h b/src/ranges/container_range.h
index 249b512..4998e59 100644
--- a/src/ranges/container_range.h
+++ b/src/ranges/container_range.h
@@ -86,7 +86,7 @@ namespace MultiArrayTools
 
 	std::vector<IndexInfo> infoVec() const;
 	
-	std::string id();
+	std::string id() const;
 	void print(size_t offset);
 	
 	template <class Exprs>
@@ -354,7 +354,7 @@ namespace MultiArrayTools
     }
     
     template <class... Indices>
-    std::string ContainerIndex<Indices...>::id()
+    std::string ContainerIndex<Indices...>::id() const
     {
 	return std::string("con") + std::to_string(IB::mId);
     }
diff --git a/src/ranges/multi_range.h b/src/ranges/multi_range.h
index 8be899c..cc55e8b 100644
--- a/src/ranges/multi_range.h
+++ b/src/ranges/multi_range.h
@@ -102,7 +102,7 @@ namespace MultiArrayTools
 
 	std::vector<IndexInfo> infoVec() const;
 	
-	std::string id();
+	std::string id() const;
 	void print(size_t offset);
 
 	template <class Exprs>
@@ -398,7 +398,7 @@ namespace MultiArrayTools
     }
     
     template <class... Indices>
-    std::string MultiIndex<Indices...>::id()
+    std::string MultiIndex<Indices...>::id() const
     {
 	return std::string("mul") + std::to_string(IB::mId);
     }
diff --git a/src/ranges/single_range.h b/src/ranges/single_range.h
index f7ac16d..be532e0 100644
--- a/src/ranges/single_range.h
+++ b/src/ranges/single_range.h
@@ -62,7 +62,7 @@ namespace MultiArrayTools
 
 	std::vector<IndexInfo> infoVec() const;
 	
-	std::string id();
+	std::string id() const;
 	void print(size_t offset);
 
 	template <class Expr>
@@ -232,7 +232,7 @@ namespace MultiArrayTools
     }
 
     template <typename U, SpaceType TYPE>
-    std::string SingleIndex<U,TYPE>::id()
+    std::string SingleIndex<U,TYPE>::id() const
     {
 	return std::string("sin") + std::to_string(IB::mId);
     }
diff --git a/src/xfor/xfor.h b/src/xfor/xfor.h
index f1dd6ff..6fb3412 100644
--- a/src/xfor/xfor.h
+++ b/src/xfor/xfor.h
@@ -9,6 +9,9 @@
 
 namespace MultiArrayHelper
 {
+
+    // 'HIDDEN FOR' CLASS for nested for loops in contractions a.s.o.
+    // (NO COUNTING OF MASTER POSITION !!!!!)
     
     template <class IndexClass, class Expr>
     class For
@@ -60,6 +63,8 @@ namespace MultiArrayHelper
  * ---   TEMPLATE CODE   --- *
  * ========================= */
 
+#include <iostream>
+
 namespace MultiArrayHelper
 {
 
@@ -67,19 +72,20 @@ namespace MultiArrayHelper
     For<IndexClass,Expr>::For(const std::shared_ptr<IndexClass>& indPtr,
 			      Expr&& expr) :
 	mIndPtr(indPtr.get()), mExpr(expr),
-	mExt(expr.rootSteps( reinterpret_cast<std::intptr_t>( mIndPtr.get() ))) {}
+	mExt(expr.rootSteps( reinterpret_cast<std::intptr_t>( mIndPtr.get() ))) { assert(mIndPtr != nullptr); }
 
     template <class IndexClass, class Expr>
     For<IndexClass,Expr>::For(const IndexClass* indPtr,
 			      Expr&& expr) :
 	mIndPtr(indPtr), mExpr(std::forward<Expr>( expr )),
-	mExt(expr.rootSteps( reinterpret_cast<std::intptr_t>( mIndPtr ) )) {}
+	mExt(expr.rootSteps( reinterpret_cast<std::intptr_t>( mIndPtr ) )) { assert(mIndPtr != nullptr); }
     
     template <class IndexClass, class Expr>
     inline void For<IndexClass,Expr>::operator()(size_t mlast,
 						 const ETuple& last) const
     {
 	auto& ind = *mIndPtr;
+	std::cout << mIndPtr << std::endl;
 	const size_t max = ind.max(); // blocking
 	for(size_t pos = ind.pos(); pos != max; ++pos){
 	    const size_t mnpos = mlast * max + pos;
@@ -93,6 +99,7 @@ namespace MultiArrayHelper
     {
 	const ETuple last;
 	auto& ind = *mIndPtr;
+	std::cout << mIndPtr << std::endl;
 	const size_t max = ind.max(); // blocking
 	for(size_t pos = ind.pos(); pos != max; ++pos){
 	    const size_t mnpos = mlast * max + pos;