diff --git a/src/include/operation/op_types.cc.h b/src/include/operation/op_types.cc.h
index ab9a302..ad673a1 100644
--- a/src/include/operation/op_types.cc.h
+++ b/src/include/operation/op_types.cc.h
@@ -170,6 +170,9 @@ namespace CNORXZ
     template <class Op>
     constexpr OpCont<T,IndexT>& OpCont<T,IndexT>::operator=(const Op& o)
     {
+	// TODO: build and execute assign expression forwarding outer index
+	// if a1 and a2 are non-expression types (like it is the case now),
+	// just do what is currently implemented
 	OI::a(mIndex, [](auto& a1, const auto& a2) { a1 = a2; }, o);
         return *this;
     }
@@ -375,7 +378,39 @@ namespace CNORXZ
 	return Operation<F,Ops...>(std::forward<F>(f), ops...);
     }
 
-    
+    template <class Tar, class Src>
+    constexpr decltype(auto) assignxpr(const Tar& tar, const Src& src)
+    {
+	static_assert(is_xpr<Tar>::value, "expected expression");
+	if constexpr(is_xpr<Src>::value){
+	    return operation([](auto& a, const auto& b) { a = b; }, tar, src);
+	}
+	else {
+	    return operation([&](auto& a) { a = src; }, tar);
+	}
+    }
+
+    template <class Tar, class Src>
+    constexpr decltype(auto) assignxpr(Tar& tar, const Src& src)
+    {
+	if constexpr(is_xpr<Tar>::value){
+	    if constexpr(is_xpr<Src>::value){
+		return operation([](auto& a, const auto& b) { a = b; }, tar, src);
+	    }
+	    else {
+		return operation([&](auto& a) { a = src; }, tar);
+	    }
+	}
+	else {
+	    if constexpr(is_xpr<Src>::value){
+		return operation([&](const auto& b) { tar = b; }, src);
+	    }
+	    else {
+		return operation([&]() { tar = src; });
+	    }
+	}
+    }
+
     /*********************
      *   Contraction     *
      *********************/
diff --git a/src/include/operation/op_types.h b/src/include/operation/op_types.h
index 548081e..2b76f28 100644
--- a/src/include/operation/op_types.h
+++ b/src/include/operation/op_types.h
@@ -212,6 +212,12 @@ namespace CNORXZ
     template <class F, class... Ops>
     constexpr decltype(auto) operation(F&& f, const Ops&... ops);
 
+    template <class Tar, class Src>
+    constexpr decltype(auto) assignxpr(const Tar& tar, const Src& src);
+
+    template <class Tar, class Src>
+    constexpr decltype(auto) assignxpr(Tar& tar, const Src& src);
+
     template <class F, class... Ops>
     struct op_size<Operation<F,Ops...>>
     { static constexpr SizeT value = ( op_size<Ops>::value + ... ); };
diff --git a/src/include/ranges/dindex.cc.h b/src/include/ranges/dindex.cc.h
index ca1f8db..6a6d0a0 100644
--- a/src/include/ranges/dindex.cc.h
+++ b/src/include/ranges/dindex.cc.h
@@ -32,13 +32,11 @@ namespace CNORXZ
 		return mI->ifor( DXpr<None>(xpr), std::forward<F>(f) );
 	    }
 	    else {
-		CXZ_ERROR("IMPLEMENT!!!");
-		return DXpr<R>();
+		return DXpr<R>( bufxpr([&](auto x){ return mI->ifor( DXpr<None>( assignxpr(x, xpr) ), NoF {} ); }) );
 	    }
 	}
 	else {
-	    CXZ_ERROR("IMPLEMENT!!!");
-	    return DXpr<R>();
+	    return DXpr<R>( bufxpr([&](auto x){ return mI->ifor( DXpr<None>( assignxpr(x, xpr) ), NoF {} ); }) );
 	}
     }
 }
diff --git a/src/include/xpr/buf_xpr.cc.h b/src/include/xpr/buf_xpr.cc.h
new file mode 100644
index 0000000..cac20ec
--- /dev/null
+++ b/src/include/xpr/buf_xpr.cc.h
@@ -0,0 +1,71 @@
+
+#include "buf_xpr.h"
+
+namespace CNORXZ
+{
+    template <typename T, class IXprF>
+    BufXpr<T,IXprF>::BufXpr(const BufXpr& in) :
+	mBuf(in.mBuf),
+	mIXprF(in.mIXprF),
+	mIXpr(mIXprF(mBuf))
+    {}
+
+    template <typename T, class IXprF>
+    BufXpr<T,IXprF>::BufXpr(BufXpr&& in) :
+	mBuf(std::move(in.mBuf)),
+	mIXprF(std::move(in.mIXprF)),
+	mIXpr(mIXprF(mBuf))
+    {}
+
+    template <typename T, class IXprF>
+    BufXpr& BufXpr<T,IXprF>::operator=(const BufXpr& in)
+    {
+	mBuf = in.mBuf;
+	mIXprF = in.mIXprF;
+	mIXpr = mIXprF(mBuf);
+	return *this;
+    }
+
+    template <typename T, class IXprF>
+    BufXpr& BufXpr<T,IXprF>::operator=(BufXpr&& in)
+    {
+	mBuf = std::move(in.mBuf);
+	mIXprF = std::move(in.mIXprF);
+	mIXpr = mIXprF(mBuf);
+	return *this;
+    }
+
+    template <typename T, class IXprF>
+    constexpr BufXpr<T,IXprF>::BufXpr(IXprF&& ixprf) :
+	mIXprF(std::forward<IXprF>(ixprf)),
+	mIXpr(mIXprF(mBuf))
+    {}
+
+    template <typename T, class IXprF>
+    template <class PosT>
+    inline decltype(auto) BufXpr<T,IXprF>::operator()(const PosT& last) const
+    {
+	mIXpr(last);
+	return mBuf;
+    }
+
+    template <typename T, class IXprF>
+    inline decltype(auto) BufXpr<T,IXprF>::operator()() const
+    {
+	mIXpr();
+	return mBuf;
+    }
+
+    template <typename T, class IXprF>
+    template <SizeT I>
+    inline decltype(auto) BufXpr<T,IXprF>::rootSteps(const IndexId<I>& id) const
+    {
+	return mIXpr.rootSteps(id);
+    }
+
+    template <typename T, class IXprF>
+    constexpr decltype(auto) bufxpr(IXprF&& ixprf)
+    {
+	return BufXpr<T,IXprF>( std::forward<IXprF>(ixprf) );
+    }
+}
diff --git a/src/include/xpr/buf_xpr.h b/src/include/xpr/buf_xpr.h
new file mode 100644
index 0000000..cd0b51f
--- /dev/null
+++ b/src/include/xpr/buf_xpr.h
@@ -0,0 +1,35 @@
+
+#include "xpr_base.h"
+
+namespace CNORXZ
+{
+    template <typename T, class IXprF>
+    class BufXpr : public XprInterface<BufXpr>
+    {
+    public:
+	BufXpr() = default;
+	BufXpr(const BufXpr& in);
+	BufXpr(BufXpr&& in);
+	BufXpr& operator=(const BufXpr& in);
+	BufXpr& operator=(BufXpr&& in);
+
+	constexpr BufXpr(IXprF&& ixprf);
+
+	template <class PosT>
+	inline decltype(auto) operator()(const PosT& last) const;
+
+	inline decltype(auto) operator()() const;
+
+	template <SizeT I>
+	inline decltype(auto) rootSteps(const IndexId<I>& id) const;
+
+    private:
+	T mBuf;
+	IXprF mIXprF; // function to create set-buffer-xpr (reference to mBuf as arg)
+	typedef decltype(mIXprF(mBuf)) IXpr;
+	IXpr mIXpr;
+    };
+
+    template <typename T, class IXprF>
+    constexpr decltype(auto) bufxpr(IXprF&& ixprf);
+}
diff --git a/src/include/xpr/xpr_base.h b/src/include/xpr/xpr_base.h
index 0b92b2e..05e7f8b 100644
--- a/src/include/xpr/xpr_base.h
+++ b/src/include/xpr/xpr_base.h
@@ -75,6 +75,12 @@ namespace CNORXZ
 	template <SizeT I>
 	inline DPos rootSteps(const IndexId<I>& id) const;
     };
+
+    template <class X>
+    struct is_xpr
+    {
+	static constexpr bool value = std::is_base_of<XprInterface<X>,X>::value;
+    };
 }
 
 #endif