diff --git a/src/include/array/array_base.cc.h b/src/include/array/array_base.cc.h
index 0bab4b2..afb6c92 100644
--- a/src/include/array/array_base.cc.h
+++ b/src/include/array/array_base.cc.h
@@ -3,9 +3,124 @@
 #define __cxz_array_base_cc_h__
 
 #include "array_base.h"
+#include "slice.h"
 
 namespace CNORXZ
 {
+    /******************************
+     *   CArrayBase (protected)   *
+     ******************************/
+
+    template <typename T>
+    template <class Index>
+    YIndex CArrayBase<T>::mkSliceIndex(const YIndex& yi, const Index& ind) const
+    {
+	// TODO: if ind.dim() < iy.dim: assume Null-Indices on missing positions;
+	static_assert(has_sub<Index>::value, "got non-mutliple index");
+	CXZ_ASSERT(yi.dim() == ind.dim(), "got index of incompatible dimension = "
+		   << ind.dim() << ", expected: " << yi.dim());
+	Vector<XIndexPtr> npack;
+	Vector<SizeT> nbs;
+	auto ypack = yi.pack();
+	auto ipack = ind.pack();
+	const auto& bs = yi.blockSizes();
+	if constexpr(has_static_sub<Index>::value){
+	    constexpr SizeT ID = index_dim<Index>::value;
+	    npack.reserve(ID);
+	    nbs.reserve(ID);
+	    iter<0,ID>( [&](auto i) {
+		const auto& ii1 = ypack[i];
+		const auto& ii2 = std::get<i>(ipack);
+		if(ii2->dim() != 0){
+		    npack.push_back( mkSliceIndex(ii1, ii2) );
+		    nbs.push_back(bs[i]);
+		}
+	    }, NoF {} );
+	}
+	else {
+	    const SizeT idim = ind.dim();
+	    npack.reserve(idim);
+	    nbs.reserve(idim);
+	    for(SizeT i = 0; i != idim; ++i){
+		const auto& ii1 = ypack[i];
+		const auto& ii2 = ipack[i];
+		if(ii2->dim() != 0){
+		    npack.push_back( mkSliceIndex(ii1, ii2) );
+		    nbs.push_back(bs[i]);
+		}
+	    }
+	}
+	return yindex(npack);
+    }
+    
+    template <typename T>
+    template <class Index>
+    XIndexPtr CArrayBase<T>::mkSliceIndex(const XIndexPtr& xi, const Sptr<Index>& ind) const
+    {
+	// TODO: if ind.dim() < iy.dim: assume Null-Indices on missing positions;
+	CXZ_ASSERT(xi->dim() == ind->dim(), "got index of incompatible dimension = "
+		   << ind->dim() << ", expected: " << xi->dim());
+	Vector<XIndexPtr> npack;
+	Vector<SizeT> nbs;
+	auto xpack = xi->pack();
+	const auto& bs = xi->blockSizes();
+	if constexpr(has_static_sub<Index>::value){
+	    auto ipack = ind->pack();
+	    constexpr SizeT ID = index_dim<Index>::value;
+	    npack.reserve(ID);
+	    nbs.reserve(ID);
+	    iter<0,ID>( [&](auto i) {
+		const auto& ii1 = xpack[i];
+		const auto& ii2 = std::get<i>(ipack);
+		const XIndexPtr si = mkSliceIndex(ii1, ii2);
+		if(si != nullptr){
+		    npack.push_back( si );
+		    nbs.push_back(bs[i]);
+		}
+	    }, NoF {} );
+	}
+	else if constexpr(has_static_sub<Index>::value){
+	    auto ipack = ind->pack();
+	    const SizeT idim = ind->dim();
+	    const SizeT xdim = xi->dim();
+	    const SizeT isize = ipack.size();
+	    const SizeT xsize = xpack.size();
+	    if(isize == 0 or xsize == 0){
+		if(idim == 0){
+		    return xi->copy();
+		}
+		else {
+		    return nullptr;
+		}
+	    }
+	    CXZ_ASSERT(isize == idim and xsize == xdim, "index error");
+	    npack.reserve(idim);
+	    nbs.reserve(idim);
+	    for(SizeT i = 0; i != idim; ++i){
+		const auto& ii1 = xpack[i];
+		const auto& ii2 = ipack[i];
+		const XIndexPtr si = mkSliceIndex(ii1, ii2);
+		if(si != nullptr){
+		    npack.push_back( si );
+		    nbs.push_back(bs[i]);
+		}
+	    }
+	}
+	else {
+	    const SizeT idim = ind->dim();
+	    if(idim == 0){
+		return xi->copy();
+	    }
+	    else {
+		return nullptr;
+	    }
+	}
+	if(npack.size() == 0){
+	    return nullptr;
+	}
+	return mkXIndex(yindexPtr(npack));
+    }
+
     /******************
      *   CArrayBase   *
      ******************/
@@ -39,13 +154,11 @@ namespace CNORXZ
     template <typename I, typename M>
     Sptr<CArrayBase<T>> CArrayBase<T>::sl(const IndexInterface<I,M>& i) const
     {
-	////auto r = mkSliceRange(i.range());
-	//auto beg = this->begin();
-	//assertCompatible(i,beg);
-	////auto bs = mkSliceBlockSizes(i, beg);
-	//auto it = beg + i.lex();
-	////return std::make_shared<CSlice>(r, this, bs, it.pos());
-	return std::make_shared<CSlice>();
+	auto beg = this->begin();
+	auto si = mkSliceIndex(beg, i);
+	auto it = beg + i.lex();
+	return std::make_shared<CSlice>(this, si, it.pos());
+	//return std::make_shared<CSlice>();
     }
 
     template <typename T>
diff --git a/src/include/array/array_base.h b/src/include/array/array_base.h
index c84af8a..9be12c4 100644
--- a/src/include/array/array_base.h
+++ b/src/include/array/array_base.h
@@ -21,6 +21,12 @@ namespace CNORXZ
 
     protected:
 	RangePtr mRange;
+
+	template <class Index>
+	YIndex mkSliceIndex(const YIndex& yi, const Index& i) const;
+
+	template <class Index>
+	XIndexPtr mkSliceIndex(const XIndexPtr& xi, const Sptr<Index>& i) const;
 	
     public:
 
@@ -92,34 +98,6 @@ namespace CNORXZ
 
     };
 
-    // to extra header file !!!:
-    template <class... Indices>
-    constexpr decltype(auto) flattenIndexPack(const Tuple<Sptr<Indices>...>& ipack)
-    {
-	constexpr SizeT D = sizeof...(Indices);
-	
-    }
-    
-    inline Vector<XIndexPtr> flattenIndexPack(const Vector<XIndexPtr>& ipack)
-    {
-	
-    }
-    
-    template <class... Indices>
-    inline SizeT indexPackDim(Tuple<Sptr<Indices>...> ipack)
-    {
-	constexpr SizeT D = sizeof...(Indices);
-	return iter<0,D>([&](const auto& i) { return std::get<i>(ipack)->dim(); },
-			 [](const auto&... e) { return (e + ...); });
-    }
-    
-    inline SizeT indexPackDim(const Vector<XIndexPtr>& ipack)
-    {
-	return std::accumulate(ipack.begin(), ipack.end(), ipack[0]->dim(),
-			       [](auto a, auto b) { return a->dim() + b->dim(); });
-    }
-
-    
 }
 
 #endif
diff --git a/src/include/ranges/index_base.h b/src/include/ranges/index_base.h
index ddea450..c00959f 100644
--- a/src/include/ranges/index_base.h
+++ b/src/include/ranges/index_base.h
@@ -86,7 +86,15 @@ namespace CNORXZ
     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, typename MetaType>
     IndexPtr<I,MetaType>& operator++(const IndexPtr<I,MetaType>& i);
 
diff --git a/src/include/ranges/index_utils.cc.h b/src/include/ranges/index_utils.cc.h
index 66f0569..c5c1967 100644
--- a/src/include/ranges/index_utils.cc.h
+++ b/src/include/ranges/index_utils.cc.h
@@ -6,71 +6,6 @@
 
 namespace CNORZX
 {
-    inline decltype(auto) getPack(const XIndexPtr& i)
-    {
-	typedef Vector<XIndexPtr> OutT;
-	OutT p = i.pack();
-	while(p.size() == 1u){
-	    p = p[0]->pack();
-	}
-	return p;
-    }
-
-    // -> base
-    template <typename... T>
-    Vector<T> mkVector(const T&... t) { return Vector<T>({t...}); }
-    
-    template <class F>
-    inline decltype(auto) indexZip(const XIndexPtr& a, const XIndexPtr& b, F&& f)
-    {
-	const auto ap = getPack(a);
-	const auto bp = getPack(b);
-	if(ap.size() == 1u or bp.size() == 1u){
-	    return mkVector( f(a, b) );
-	}
-	else {
-	    return indexPackZip(ap, bp, std::forward<F>(f));
-	}
-    }
-    
-    template <class F>
-    inline decltype(auto) indexPackZip(const Vector<XIndexPtr>& a, const Vector<XIndexPtr>& b, F&& f)
-    {
-	if(a.size() > b.size()) {
-	    Vector<XIndexPtr> bn;
-	    for(const auto& x: b){
-		auto p = getPack(x);
-		if(p.size() == 0){
-		    bn.push_back(x);
-		}
-		else {
-		    bn.insert(bn.end(), p.begin(), p.end());
-		}
-	    }
-	    return indexPackZip(a, bn, std::forward<F>(f));
-	}
-	else if(a.size() < b.size()) {
-	    Vector<XIndexPtr> an;
-	    for(const auto& x: a){
-		auto p = getPack(x);
-		if(p.size() == 0){
-		    an.push_back(x);
-		}
-		else {
-		    an.insert(bn.end(), p.begin(), p.end());
-		}
-	    }
-	    return indexPackZip(an, b, std::forward<F>(f));
-	}
-	else {
-	    typedef decltype(indexZip(a[0], b[0], std::forward<T>(f))) OutT;
-	    OutT o(a.size());
-	    std::transform(o.begin(), o.end(), a.begin(), b.begin(),
-			   [](const auto& ax, const auto& bx) { F fc = f; return indexZip(ax, bx, std::move(fc)); });
-	    return o;
-	}
-    }
-
     template <class Index>
     constexpr decltype(auto) getIndexDepth(const Index& ind)
     {
diff --git a/src/include/ranges/index_utils.h b/src/include/ranges/index_utils.h
index cafaa2f..4c2ab55 100644
--- a/src/include/ranges/index_utils.h
+++ b/src/include/ranges/index_utils.h
@@ -6,19 +6,13 @@
 
 namespace CNORZX
 {
-    inline decltype(auto) getPack(const XIndexPtr& i);
-    
-    template <class F>
-    inline decltype(auto) indexZip(const XIndexPtr& a, const XIndexPtr& b, F&& f);
-
-    template <class F>
-    inline decltype(auto) indexPackZip(const Vector<XIndexPtr>& a, const Vector<XIndexPtr>& b, F&& f);
-
     template <class Index>
     constexpr decltype(auto) getIndexDepth(const Index& ind);
 
     template <class Index, typename IntT>
     constexpr decltype(auto) getDimension(const Index& ind, IntT depth);
+
+    
 }
 
 #endif
diff --git a/src/include/ranges/mrange.cc.h b/src/include/ranges/mrange.cc.h
index 333e533..0f3c9b7 100644
--- a/src/include/ranges/mrange.cc.h
+++ b/src/include/ranges/mrange.cc.h
@@ -434,50 +434,6 @@ namespace CNORXZ
 	return mIPack;
     }
 
-    template <class BlockType, class... Indices>
-    template <class Index, class F, class G>
-    constexpr decltype(auto) GMIndex<BlockType,Indices...>::zip(const Index& ind, const F& f, const G& g) const
-    {
-	static_assert(is_index<Index>::value, "got non-index type");
-	if constexpr(has_static_sub<Index>::value){
-	    static_assert(index_dim<Index>::value == NI,
-			  "got static-dimensional index with wrong dimension");
-	    if constexpr(std::is_same<G,NoF>::value or std::is_same<F,NoF>::value){
-		iter<0,NI>( [&](auto i) { return std::get<i>(mIPack)->zip(*std::get<i>(ind.pack()), f); },
-			    NoF {} );
-		f(*this, ind);
-		return;
-	    }
-	    else {
-		return iter<0,NI>( [&](auto i) { return std::get<i>(mIPack)->zip(*std::get<i>(ind.pack()), f); },
-				   [](auto... e) { return g(std::make_tuple(e...), f(*this, ind)); } );
-	    }
-	}
-	else if constexpr(has_sub<Index>::value){
-	    CXZ_ASSERT(ind.dim() == NI, "got index with wrong dimension = " << ind.dim()
-		       << ", expected: " << NI);
-	    if constexpr(std::is_same<G,NoF>::value or std::is_same<F,NoF>::value){
-		iter<0,NI>( [&](auto i) { return std::get<i>(mIPack)->zip(*ind.pack()[i],f); },
-			    NoF {} );
-		f(*this, ind);
-		return;
-	    }
-	    else {
-		return iter<0,NI>( [&](auto i) { return std::get<i>(mIPack)->zip(*ind.pack()[i],f); },
-				   [](auto... e) { return g(std::make_tuple(e...), f(*this, ind)); } );
-	    }
-	}
-	else {
-	    if constexpr(std::is_same<F,NoF>::value){
-		f(*this, ind);
-		return;
-	    }
-	    else {
-		return f(*this, ind);
-	    }
-	}
-    }
-
     template <class BlockType, class... Indices>
     const auto& GMIndex<BlockType,Indices...>::blockSizes() const
     {
@@ -496,7 +452,7 @@ namespace CNORXZ
     }
 
     template <class BlockType, class... Indices>
-    GMIndex& GMIndex<BlockType,Indices...>::setBlockSizes(const BlockType& bs)
+    GMIndex<BlockType,Indices...>& GMIndex<BlockType,Indices...>::setBlockSizes(const BlockType& bs)
     {
 	if constexpr(not std::is_same<BlockType,None>::value){
 	    mBlockSizes = bs;
@@ -505,10 +461,20 @@ namespace CNORXZ
     }
 
     template <class BT1, class BT2, class... Indices>
-    decltype(auto) replaceBlockSize(const BT1& bs1, const Sptr<GMIndex<BT2,Indices...>>& gmi)
+    decltype(auto) replaceBlockSizes(const BT1& bs1, const Sptr<GMIndex<BT2,Indices...>>& gmi)
     {
 	return iter<0,sizeof...(Indices)>
-	    ( [&](auto i) { return std::get<i>(gmi.pack()); },
+	    ( [&](auto i) { return std::get<i>(gmi->pack()); },
+	      [&](const auto&... e) { return std::make_shared<GMIndex<BT1,Indices...>>
+		    ( bs1, e... ); } );
+    }
+
+    template <class BT1, class BT2, class... Indices>
+    decltype(auto) replaceBlockSizes(const BT1& bs1,
+				     const Sptr<IndexInterface<GMIndex<BT2,Indices...>,typename GMIndex<BT2,Indices...>::MetaType>>& gmi)
+    {
+	return iter<0,sizeof...(Indices)>
+	    ( [&](auto i) { return std::get<i>(gmi->THIS().pack()); },
 	      [&](const auto&... e) { return std::make_shared<GMIndex<BT1,Indices...>>
 		    ( bs1, e... ); } );
     }
diff --git a/src/include/ranges/mrange.h b/src/include/ranges/mrange.h
index b89f5e9..1df0ce2 100644
--- a/src/include/ranges/mrange.h
+++ b/src/include/ranges/mrange.h
@@ -70,9 +70,6 @@ namespace CNORXZ
 	GMIndex& operator()(const Sptr<MIndex<Indices...>>& mi);
 	GMIndex& operator()();
 
-	template <class Index, class F = NoF, class G = NoF>
-	constexpr decltype(auto) zip(const Index& ind, const F& f, const G& g) const; // also non-const version !!!
-
 	const IndexPack& pack() const;
 	const auto& blockSizes() const;
 	const auto& lexBlockSizes() const;
@@ -113,7 +110,11 @@ namespace CNORXZ
     };
 
     template <class BT1, class BT2, class... Indices>
-    decltype(auto) replaceBlockSize(const BT1& bs1, const Sptr<GMIndex<BT2,Indices...>>& gmi);
+    decltype(auto) replaceBlockSizes(const BT1& bs1, const Sptr<GMIndex<BT2,Indices...>>& gmi);
+
+    template <class BT1, class BT2, class... Indices>
+    decltype(auto) replaceBlockSizes(const BT1& bs1,
+				     const Sptr<IndexInterface<GMIndex<BT2,Indices...>,typename GMIndex<BT2,Indices...>::MetaType>>& gmi);
     
     template <class BT1, class... Is1, class BT2, class... Is2>
     decltype(auto) operator*(const Sptr<GMIndex<BT1,Is1...>>& a, const Sptr<GMIndex<BT2,Is2...>>& b);
@@ -132,6 +133,14 @@ namespace CNORXZ
     struct index_dim<MIndex<Indices...>>
     { static constexpr SizeT value = sizeof...(Indices); };
 
+    template <class... Indices>
+    struct has_sub<MIndex<Indices...>>
+    { static constexpr bool value = true; };
+
+    template <class... Indices>
+    struct has_static_sub<MIndex<Indices...>>
+    { static constexpr bool value = true; };
+
     template <class... Indices>
     constexpr decltype(auto) mindex(const Sptr<Indices>&... is);
 
diff --git a/src/include/ranges/xindex.cc.h b/src/include/ranges/xindex.cc.h
index f4dc5a5..56a48f8 100644
--- a/src/include/ranges/xindex.cc.h
+++ b/src/include/ranges/xindex.cc.h
@@ -133,14 +133,14 @@ namespace CNORXZ
 	if constexpr(has_static_sub<Index>::value){
 	    constexpr SizeT D = index_dim<Index>::value;
 	    return iter<0,D>
-		( [&](auto i) { return mkXIndex(std::get<i>(mI->pack())); },
-		  [](const auto&... e) { return { e ... }; } );
+		( [&](auto i) { return mkXIndex(std::get<i>(mI->THIS().pack())); },
+		  [](const auto&... e) { return Vector<XIndexPtr>({ e ... }); } );
 	}
 	else if constexpr(has_sub<Index>::value){
-	    return mI->pack();
+	    return mI->THIS().pack();
 	}
 	else {
-	    return {};
+	    return Vector<XIndexPtr>();
 	}
     }
 
@@ -149,15 +149,16 @@ namespace CNORXZ
     {
 	if constexpr(has_static_sub<Index>::value){
 	    constexpr SizeT D = index_dim<Index>::value;
+	    const auto& bs = mI->THIS().blockSizes();
 	    return iter<0,D>
-		( [&](auto i) { return std::get<i>(mI->blockSizes()); },
-		  [](const auto&... e) { return Vector<SizeT>( { e... } ); } );
+		( [&](auto i) { return std::get<i>(bs); },
+		  [](const auto&... e) { return Vector<SizeT>( { static_cast<SizeT>(e)... } ); } );
 	}
 	else if constexpr(has_sub<Index>::value) {
-	    return mI->blockSizes();
+	    return mI->THIS().blockSizes();
 	}
 	else {
-	    return {};
+	    return Vector<SizeT>();
 	}
     }
 
@@ -168,19 +169,19 @@ namespace CNORXZ
 	    constexpr SizeT D = index_dim<Index>::value;
 	    CXZ_ASSERT(bs.size() == D,
 		       "got block sizes of wrong dimension: " << bs.size() << " vs " << D);
-	    typedef decltype(mI->blockSizes()) BT;
-	    Arr<SizeT,D> arr;
+	    typedef decltype(mI->THIS().blockSizes()) BT;
+	    Arr<UPos,D> arr;
 	    std::copy_n(bs.begin(), D, arr.begin());
-	    if constexpr(std::is_same<BT,Arr<SizeT,D>>::value){
-		mI->setBlockSizes(arr);
+	    if constexpr(std::is_same<BT,Arr<UPos,D>>::value){
+		mI->THIS().setBlockSizes(arr);
 		return nullptr;
 	    }
 	    else {
-		return replaceBlockSizes(arr, mI);
+		return mkXIndex(replaceBlockSizes(arr, mI));
 	    }
 	}
 	else if constexpr(has_sub<Index>::value) {
-	    mI->setBlockSizes(bs);
+	    mI->THIS().setBlockSizes(bs);
 	    return nullptr;
 	}
 	else {
diff --git a/src/include/ranges/xindex.h b/src/include/ranges/xindex.h
index 987d675..4da6a42 100644
--- a/src/include/ranges/xindex.h
+++ b/src/include/ranges/xindex.h
@@ -46,6 +46,7 @@ namespace CNORXZ
 
 	virtual DXpr<SizeT> ifor(const DXpr<SizeT>& xpr,
 				 std::function<SizeT(SizeT,SizeT)>&& f) const = 0;
+
     };
 
     //Sptr<XIndexBase>& operator++(Sptr<XIndexBase>& i);
@@ -103,6 +104,10 @@ namespace CNORXZ
 
     };
 
+    template <>
+    struct has_sub<XIndexBase>
+    { static constexpr bool value = true; };
+    
     template <class Index>
     XIndexPtr mkXIndex(const Sptr<Index>& i);
     
diff --git a/src/include/ranges/yrange.h b/src/include/ranges/yrange.h
index a9b96da..b88027a 100644
--- a/src/include/ranges/yrange.h
+++ b/src/include/ranges/yrange.h
@@ -85,6 +85,9 @@ namespace CNORXZ
 	UPos mLMax = 0;
     };
 
+    YIndex yindex(const Vector<XIndexPtr>& is);
+    Sptr<YIndex> yindexPtr(const Vector<XIndexPtr>& is);
+
     class YRangeFactory : public RangeFactoryBase
     {
     public:
diff --git a/src/include/xpr/pos_type.cc.h b/src/include/xpr/pos_type.cc.h
index 40dffa5..8adf78a 100644
--- a/src/include/xpr/pos_type.cc.h
+++ b/src/include/xpr/pos_type.cc.h
@@ -111,6 +111,12 @@ namespace CNORXZ
 	return UPos(mExt + in.val());
     }
 
+    template <class PosT>
+    constexpr UPos UPos::operator-(const PosT& in) const
+    {
+	return UPos(mExt - in.val());
+    }
+
     constexpr SPos<0> UPos::operator*(const SPos<0>& a) const
     {
 	return SPos<0>();
diff --git a/src/include/xpr/pos_type.h b/src/include/xpr/pos_type.h
index cac728f..b7eaa68 100644
--- a/src/include/xpr/pos_type.h
+++ b/src/include/xpr/pos_type.h
@@ -54,6 +54,9 @@ namespace CNORXZ
 	template <class PosT>
 	constexpr UPos operator+(const PosT& a) const;
 
+	template <class PosT>
+	constexpr UPos operator-(const PosT& a) const;
+
 	constexpr SPos<0> operator*(const SPos<0>& a) const;
 
         template <class PosT>
diff --git a/src/lib/ranges/yrange.cc b/src/lib/ranges/yrange.cc
index dfc97e2..cc6ecbf 100644
--- a/src/lib/ranges/yrange.cc
+++ b/src/lib/ranges/yrange.cc
@@ -378,7 +378,20 @@ namespace CNORXZ
 	return *this;
     }
 
-    
+    /****************************
+     *   non-member functions   *
+     ****************************/
+
+    YIndex yindex(const Vector<XIndexPtr>& is)
+    {
+	return YIndex(is);
+    }
+
+    Sptr<YIndex> yindexPtr(const Vector<XIndexPtr>& is)
+    {
+	return std::make_shared<YIndex>(is);
+    }
+
     /**********************
      *   YRangeFactory    *
      **********************/