diff --git a/TODO b/TODO
index 0d70161..f76be28 100644
--- a/TODO
+++ b/TODO
@@ -10,14 +10,10 @@ include/ranges/index_base.cc.h@110: "if this assert never applies, remove mPtrId
 include/ranges/mrange.cc.h@633: "TODO: ZRange (meta and index pos static!)" [long]
 include/ranges/urange.cc.h@366: "else general transform using DType (better than nothing), to be implemented" [urgent]
 include/ranges/urange.cc.h@430: "else general transform using DType (better than nothing), to be implemented" [urgent]
-include/ranges/prange.cc.h@193: "implement" [urgent]
-include/ranges/prange.cc.h@325: "implement" [urgent]
-include/ranges/xindex.cc.h@183: "IMPLEMENT" [urgent]
 include/xpr/for.cc.h@314: "check for write access" [check]
 include/ranges/srange.cc.h@292: "TODO: check for selected static sizes of SRange -> return SRange" [long]
 lib/ranges/crange.cc@114: "preliminary solution (TODO: implement xpr that simply returns PosT value)" [long]
-lib/ranges/yrange.cc@348: "IMPLEMENT" [urgent]
 
 opt/hdf5/lib/h5_group.cc@166: "IMPLEMENT" [urgent]
 opt/hdf5/include/h5_group.cc.h@34: "not implemented" [urgent]
-opt/hdf5/lib/h5_table.cc@127: "not implemented" [urgent]
\ No newline at end of file
+opt/hdf5/lib/h5_table.cc@127: "not implemented" [urgent]
diff --git a/src/include/ranges/crange.h b/src/include/ranges/crange.h
index 07f6352..e6934d6 100644
--- a/src/include/ranges/crange.h
+++ b/src/include/ranges/crange.h
@@ -215,6 +215,16 @@ namespace CNORXZ
 	/** cast the range */
 	static Sptr<CRange> func(const RangePtr& r);
     };
+
+    /** ***
+	CIndex can be used as expression
+	@see index_expression_exists
+     */    
+    template <>
+    struct index_expression_exists<CIndex>
+    {
+	static constexpr bool value = true;
+    };
 }
 
 #endif
diff --git a/src/include/ranges/dindex.h b/src/include/ranges/dindex.h
index 95906bc..bdfd741 100644
--- a/src/include/ranges/dindex.h
+++ b/src/include/ranges/dindex.h
@@ -62,12 +62,9 @@ namespace CNORXZ
 	String stringMeta() const;
 	DType meta() const;
 	DIndex& at(const DType& meta);
-	DXpr<SizeT> xpr(const Sptr<DIndex>& _this) const;
 	RangePtr prange(const DIndex& end) const;
 	Vector<SizeT> deepFormat() const;
 	
-	//DXpr<None> ifor(const DXpr<None>& xpr, NoF&& f) const;
-
 	template <class Xpr, class F>
 	decltype(auto) ifor(const Xpr& xpr, F&& f) const;
 	
diff --git a/src/include/ranges/eindex.h b/src/include/ranges/eindex.h
index 0d8b368..f7c0bc7 100644
--- a/src/include/ranges/eindex.h
+++ b/src/include/ranges/eindex.h
@@ -43,6 +43,16 @@ namespace CNORXZ
     {
 	static constexpr bool value = true;
     };
+
+    /** ***
+	EIndex can be used as expression
+	@see index_expression_exists
+     */    
+    template <typename MetaT, SizeT S, SizeT L>
+    struct index_expression_exists<EIndex<MetaT,S,L>>
+    {
+	static constexpr bool value = true;
+    };
     
     template <typename MetaT, SizeT S, SizeT L, class I1>
     decltype(auto) operator*(const Sptr<EIndex<MetaT,S,L>>& a, const Sptr<I1>& b);
diff --git a/src/include/ranges/index_base.cc.h b/src/include/ranges/index_base.cc.h
index 38edb69..bc2dc9a 100644
--- a/src/include/ranges/index_base.cc.h
+++ b/src/include/ranges/index_base.cc.h
@@ -143,6 +143,19 @@ namespace CNORXZ
 	return std::make_shared<IndexInterface<I,MetaType>>( *i - n );
     }
 
+    template <class I>
+    Sptr<I> moveToPtr(I&& i)
+    {
+	return std::make_shared<I>(std::forward(i));
+    }
+
+    template <class I>
+    decltype(auto) xpr(const Sptr<I>& i)
+    {
+	static_assert(is_index<I>::value, "got non-index type");
+	static_assert(index_expression_exists<I>::value, "expression for given index type does not exist");
+	return i->xpr(i);
+    }
 }
 
 #endif
diff --git a/src/include/ranges/index_base.h b/src/include/ranges/index_base.h
index a246e3f..bcf6189 100644
--- a/src/include/ranges/index_base.h
+++ b/src/include/ranges/index_base.h
@@ -164,12 +164,6 @@ namespace CNORXZ
 	 */
 	I& at(const MetaType& meta) { return THIS().at(meta); }
 
-	/** create expression on this index
-
-	    @param _this pointer to this index
-	 */
-	decltype(auto) xpr(const Sptr<I>& _this) const { return THIS().xpr(_this); }
-
 	/** create partial range starting at this index' position and ending
 	    at the position of input index. The end position is included!
 	    @param end end index
@@ -210,34 +204,7 @@ namespace CNORXZ
 	PtrId mPtrId = 0;
     };
 
-    template <class I>
-    struct is_index
-    { static constexpr bool value = std::is_base_of<IndexInterface<I,typename I::MetaType>,I>::value; };
     
-    template <class I>
-    struct index_has_const_size
-    { static constexpr bool value = false; };
-
-    template <class I>
-    struct index_const_size
-    { static constexpr SizeT value = 0; };
-
-    template <class I>
-    struct index_dim
-    { static constexpr SizeT value = 1; };
-
-    template <class T>
-    struct has_sub
-    { static constexpr bool value = false; };
-
-    template <class T>
-    struct has_static_sub
-    { static constexpr bool value = false; };
-
-    template <class I>
-    struct index_is_multi
-    { static constexpr bool value = false; };
-
     template <class I, typename MetaType>
     IndexPtr<I,MetaType>& operator++(const IndexPtr<I,MetaType>& i);
 
@@ -252,7 +219,10 @@ namespace CNORXZ
     IndexPtr<I,MetaType> operator-(const IndexPtr<I,MetaType>& i, Int n);
 
     template <class I>
-    Sptr<I> moveToPtr(I&& i) { return std::make_shared<I>(std::forward(i)); }
+    Sptr<I> moveToPtr(I&& i);
+
+    template <class I>
+    decltype(auto) xpr(const Sptr<I>& i);
 }
 
 #endif
diff --git a/src/include/ranges/index_traits.h b/src/include/ranges/index_traits.h
new file mode 100644
index 0000000..5f1f944
--- /dev/null
+++ b/src/include/ranges/index_traits.h
@@ -0,0 +1,92 @@
+// -*- C++ -*-
+/**
+   
+   @file include/ranges/index_traits.h
+   @brief index traits
+
+   Copyright (c) 2022 Christian Zimmermann. All rights reserved.
+   Mail: chizeta@f3l.de
+   
+**/
+
+#ifndef __cxz_index_traits__
+#define __cxz_index_traits__
+
+namespace CNORXZ
+{
+    /** *****
+	check if given type is index-type
+
+	@tparam I type to be checked
+     **/
+    template <class I>
+    struct is_index
+    { static constexpr bool value = std::is_base_of<IndexInterface<I,typename I::MetaType>,I>::value; };
+    
+    /** *****
+	check if given type is index-type with a static range size
+
+	@tparam I type to be checked
+     **/
+    template <class I>
+    struct index_has_const_size
+    { static constexpr bool value = false; };
+
+    /** *****
+	return static range size of an index (0 if there is no static size)
+
+	@tparam I type to be checked
+     **/
+    template <class I>
+    struct index_const_size
+    { static constexpr SizeT value = 0; };
+
+    /** *****
+	return the static dimension of an index (1 if index is not statically multi-dimensional)
+	
+	@tparam I type to be checked
+     **/
+    template <class I>
+    struct index_dim
+    { static constexpr SizeT value = 1; };
+
+    /** *****
+	check if given type is index-type with sub-indices
+
+	@tparam I type to be checked
+     **/
+    template <class T>
+    struct has_sub
+    { static constexpr bool value = false; };
+
+    /** *****
+	check if given type is index-type with static sub-indices
+
+	@tparam I type to be checked
+     **/
+    template <class T>
+    struct has_static_sub
+    { static constexpr bool value = false; };
+
+    /** *****
+	check if given type is a statically multi-index-type 
+
+	@tparam I type to be checked
+     **/
+    template <class I>
+    struct index_is_multi
+    { static constexpr bool value = false; };
+
+    /** *****
+	check if given type is index-type that can be used in an expression,
+	i.e. has a member function xpr()
+
+	@tparam I type to be checked
+     **/
+    template <class I>
+    struct index_expression_exists
+    { static constexpr bool value = false; };
+
+}
+
+#endif
diff --git a/src/include/ranges/lindex.h b/src/include/ranges/lindex.h
index cf550b7..283d347 100644
--- a/src/include/ranges/lindex.h
+++ b/src/include/ranges/lindex.h
@@ -49,6 +49,16 @@ namespace CNORXZ
 	static constexpr bool value = is_index<Index>::value; 
     };
 
+    /** ***
+	LIndex can be used as expression if this is case for its base type
+	@see index_expression_exists
+     */    
+    template <class Index, SizeT L>
+    struct index_expression_exists<LIndex<Index,L>>
+    {
+	static constexpr bool value = index_expression_exists<Index>::value;
+    };
+
     template <class Index, SizeT L, class I1>
     decltype(auto) operator*(const Sptr<LIndex<Index,L>>& a, const Sptr<I1>& b);
 
diff --git a/src/include/ranges/mrange.h b/src/include/ranges/mrange.h
index aa30d7c..5faf4f1 100644
--- a/src/include/ranges/mrange.h
+++ b/src/include/ranges/mrange.h
@@ -234,6 +234,16 @@ namespace CNORXZ
     {
 	static Sptr<MRange<Ranges...>> func(const RangePtr& r);
     };
+
+    /** ***
+	MIndex can be used as expression if all its sub-indices can be used as expression
+	@see index_expression_exists
+     */    
+    template <class... Indices>
+    struct index_expression_exists<MIndex<Indices...>>
+    {
+	static constexpr bool value = (index_expression_exists<Indices>::value and ...);
+    };
 }
 
 #endif
diff --git a/src/include/ranges/ranges.h b/src/include/ranges/ranges.h
index 36f51bc..5cff132 100644
--- a/src/include/ranges/ranges.h
+++ b/src/include/ranges/ranges.h
@@ -12,6 +12,7 @@
 
 #include "range_base.h"
 #include "index_base.h"
+#include "index_traits.h"
 #include "mrange.h"
 #include "xindex.h"
 #include "yrange.h"
diff --git a/src/include/ranges/srange.h b/src/include/ranges/srange.h
index 0ece1f7..6325126 100644
--- a/src/include/ranges/srange.h
+++ b/src/include/ranges/srange.h
@@ -134,6 +134,15 @@ namespace CNORXZ
 	static Sptr<SRange<MetaT,S>> func(const RangePtr& r);
     };
     
+    /** ***
+	SIndex can be used as expression
+	@see index_expression_exists
+     */    
+    template <typename MetaT, SizeT S>
+    struct index_expression_exists<SIndex<MetaT,S>>
+    {
+	static constexpr bool value = true;
+    };
 }
 
 #endif
diff --git a/src/include/ranges/urange.h b/src/include/ranges/urange.h
index 7d5dade..aec0577 100644
--- a/src/include/ranges/urange.h
+++ b/src/include/ranges/urange.h
@@ -144,6 +144,16 @@ namespace CNORXZ
 
     template <typename MetaT>
     RangePtr urange(const Vector<MetaT>& space);
+
+    /** ***
+	UIndex can be used as expression
+	@see index_expression_exists
+     */    
+    template <typename MetaT>
+    struct index_expression_exists<UIndex<MetaT>>
+    {
+	static constexpr bool value = true;
+    };
 }
 
 #endif
diff --git a/src/include/ranges/xindex.cc.h b/src/include/ranges/xindex.cc.h
index ec1575f..ca866e4 100644
--- a/src/include/ranges/xindex.cc.h
+++ b/src/include/ranges/xindex.cc.h
@@ -177,15 +177,6 @@ namespace CNORXZ
 	return *this;
     }
 
-    template <class Index, typename Meta>
-    DXpr<SizeT> XIndex<Index,Meta>::xpr(const XIndexPtr& _this) const
-    {
-	CXZ_ERROR("IMPLEMENT!!!");
-	auto xthis = std::dynamic_pointer_cast<Index>(_this);
-	//mI->xpr(xthis)
-	return DXpr<SizeT>(  );
-    }
-
     template <class Index, typename Meta>
     DXpr<None> XIndex<Index,Meta>::ifor(const DXpr<None>& xpr, NoF&& f) const
     {
diff --git a/src/include/ranges/xindex.h b/src/include/ranges/xindex.h
index f16d67f..d7bed28 100644
--- a/src/include/ranges/xindex.h
+++ b/src/include/ranges/xindex.h
@@ -56,7 +56,6 @@ namespace CNORXZ
 	virtual String stringMeta() const = 0;
 	virtual DType meta() const = 0;
 	virtual XIndexBase& at(const DType& meta) = 0;
-	virtual DXpr<SizeT> xpr(const XIndexPtr& _this) const = 0;
 
 	virtual DXpr<None> ifor(const DXpr<None>& xpr, NoF&& f) const = 0;
 
@@ -109,7 +108,6 @@ namespace CNORXZ
 	virtual String stringMeta() const override final;
 	virtual DType meta() const override final;
 	virtual XIndexBase& at(const DType& meta) override final;
-	virtual DXpr<SizeT> xpr(const XIndexPtr& _this) const override final;
 
 	virtual DXpr<None> ifor(const DXpr<None>& xpr, NoF&& f) const override final;
 
diff --git a/src/include/ranges/yrange.h b/src/include/ranges/yrange.h
index ee2987f..49dd8b6 100644
--- a/src/include/ranges/yrange.h
+++ b/src/include/ranges/yrange.h
@@ -67,7 +67,6 @@ namespace CNORXZ
 	String stringMeta() const;
 	Vector<DType> meta() const;
 	YIndex& at(const Vector<DType>& meta);
-	DXpr<SizeT> xpr(const Sptr<YIndex>& _this) const;
 
 	DXpr<None> ifor(const DXpr<None>& xpr, NoF&& f) const;
 
diff --git a/src/lib/ranges/dindex.cc b/src/lib/ranges/dindex.cc
index 534b2ec..5e16be6 100644
--- a/src/lib/ranges/dindex.cc
+++ b/src/lib/ranges/dindex.cc
@@ -167,11 +167,6 @@ namespace CNORXZ
 	return *this;
     }
 
-    DXpr<SizeT> DIndex::xpr(const Sptr<DIndex>& _this) const
-    {
-	return mI->xpr(_this->xptr());
-    }
-
     RangePtr DIndex::prange(const DIndex& end) const
     {
 	return mI->prange( end.xptr() );
diff --git a/src/lib/ranges/yrange.cc b/src/lib/ranges/yrange.cc
index 147857f..16864f2 100644
--- a/src/lib/ranges/yrange.cc
+++ b/src/lib/ranges/yrange.cc
@@ -343,12 +343,6 @@ namespace CNORXZ
 	return *this;
     }
 
-    DXpr<SizeT> YIndex::xpr(const Sptr<YIndex>& _this) const
-    {
-	CXZ_ERROR("IMPLEMENT!!!" << _this->lmax().val());
-	return DXpr<SizeT>();
-    }
-
     DXpr<None> YIndex::ifor(const DXpr<None>& xpr, NoF&& f) const
     {
 	return mkIFor(0, xpr, std::forward<NoF>(f));