diff --git a/src/include/ranges/crange.h b/src/include/ranges/crange.h
index 707b796..45d2ef6 100644
--- a/src/include/ranges/crange.h
+++ b/src/include/ranges/crange.h
@@ -111,7 +111,7 @@ namespace CNORXZ
 	SizeT deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
-	CIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
+	CIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s);
 	
 	/** @copydoc IndexInterface::ifor() */
 	template <class Xpr, class F = NoF>
diff --git a/src/include/ranges/dindex.h b/src/include/ranges/dindex.h
index d0402d1..5511625 100644
--- a/src/include/ranges/dindex.h
+++ b/src/include/ranges/dindex.h
@@ -67,7 +67,7 @@ namespace CNORXZ
 	Vector<SizeT> deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
-	DIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
+	DIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s);
 	
 	template <class Xpr, class F>
 	decltype(auto) ifor(const Xpr& xpr, F&& f) const;
diff --git a/src/include/ranges/index_base.cc.h b/src/include/ranges/index_base.cc.h
index e9d5f2e..4ba1774 100644
--- a/src/include/ranges/index_base.cc.h
+++ b/src/include/ranges/index_base.cc.h
@@ -157,17 +157,6 @@ namespace CNORXZ
 	return i->xpr(i);
     }
 
-    template <class I>
-    decltype(auto) reformat(const Sptr<I>& i, const Vector<SizeT>& f, const Vector<SizeT>& s)
-    {
-	if constexpr(has_sub<I>::value){
-	    return moveToPtr( i->reformat(f,s) );
-	}
-	else {
-	    i->reformat(f,s); // checks
-	    return i;
-	}
-    }
 }
 
 #endif
diff --git a/src/include/ranges/index_base.h b/src/include/ranges/index_base.h
index ef59ec7..e13b027 100644
--- a/src/include/ranges/index_base.h
+++ b/src/include/ranges/index_base.h
@@ -179,9 +179,8 @@ namespace CNORXZ
 	/** reformat index, create new index instance
 	    @param f new format
 	    @param s new sub-index sizes
-	    @return new reformatted index instance
 	 */
-	decltype(auto) reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const { return THIS().reformat(f,s); }
+	I& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) { return THIS().reformat(f,s); }
 	
 	/** create a for-loop expression
 
@@ -234,9 +233,6 @@ namespace CNORXZ
     template <class I>
     decltype(auto) xpr(const Sptr<I>& i);
 
-    // do not copy single-indices:
-    template <class I>
-    decltype(auto) reformat(const Sptr<I>& i, const Vector<SizeT>& f, const Vector<SizeT>& s);
 }
 
 #endif
diff --git a/src/include/ranges/index_format.h b/src/include/ranges/index_format.h
index 21353ca..9f80d32 100644
--- a/src/include/ranges/index_format.h
+++ b/src/include/ranges/index_format.h
@@ -24,6 +24,8 @@ namespace CNORXZ
     class MFormat
     {
     public:
+	typedef Arr<UPos,N> InputType;
+	
 	SP_DEFAULT_MEMBERS(constexpr,MFormat);
 	explicit constexpr MFormat(const Arr<UPos,N>& b);
 
@@ -50,6 +52,8 @@ namespace CNORXZ
     class GMFormat
     {
     public:
+	typedef Tuple<PosT...> InputType;
+
 	SP_DEFAULT_MEMBERS(constexpr,GMFormat);
 	explicit constexpr GMFormat(const Tuple<PosT...>& b);
 	explicit constexpr GMFormat(Tuple<PosT...>&& b);
@@ -78,6 +82,8 @@ namespace CNORXZ
     class YFormat
     {
     public:
+	typedef Vector<UPos> InputType;
+	
 	DEFAULT_MEMBERS(YFormat);
 	explicit YFormat(const Vector<UPos>& b);
 
diff --git a/src/include/ranges/mrange.cc.h b/src/include/ranges/mrange.cc.h
index 621ce7b..7fb78b7 100644
--- a/src/include/ranges/mrange.cc.h
+++ b/src/include/ranges/mrange.cc.h
@@ -539,41 +539,45 @@ namespace CNORXZ
     }
 
     template <class FormatT, class... Indices>
-    decltype(auto)
-    GMIndex<FormatT,Indices...>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    GMIndex<FormatT,Indices...>&
+    GMIndex<FormatT,Indices...>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
-	CXZ_ASSERT(f.size() == s.size(), "input error: f.size() != s.size()");
-	// f: input format
-	// s: input sizes
-	SizeT j = 0;
-	SizeT j0 = 0;
-	Arr<UPos,NI> nformat;
-	auto npack = iter<0,NI>( [&](auto i) {
-	    SizeT si = 1;
-	    if(mIPack[i]->lmax().val() == 1){
-		//std::get<i>(npack) = mIPack[i];
-		return mIPack[i];
-	    }
-	    // CHECK!!!
-	    for(; si < mIPack[i]->lmax().val(); ++j){
-		si *= s[i];
-		CXZ_ASSERT(j < f.size(), "incompatible index formats");
-	    }
-	    CXZ_ASSERT(si == mIPack[i]->lmax().val(),
-		       "incompatible index formats: " << toString(s) << " vs " //!!!
-		       );
-	    Vector<SizeT> nf(j-j0);
-	    Vector<SizeT> ns(j-j0);
-	    std::copy(f.begin()+j0,f.begin()+j,nf.begin());
-	    nformat[i] = *std::min_element(nf.begin(), nf.end());
-	    std::for_each(nf.begin(), nf.end(), [&](SizeT& x)
-	    { CXZ_ASSERT(x % nformat[i].val() == 0, "incompatible"); x /= nformat[i].val(); } );
-	    std::copy(s.begin()+j0,s.begin()+j,ns.begin());
-	    return CNORXZ::reformat(mIPack[i],nf,ns);
-	}, [](const auto&... e) { return std::make_tuple( e... ); } );
-	GMIndex<MFormat<NI>,Indices...> oi { MFormat<NI>(nformat),SPack<Indices...>(npack) };
-	oi = lex();
-	return oi;
+	if constexpr(std::is_same<FormatT,None>::value){
+	    CXZ_ASSERT(CNORXZ::formatIsTrivial(f,s),
+		       "cannot reformat MIndex with format type = None");
+	    return *this;
+	}
+	else {
+	    CXZ_ASSERT(f.size() == s.size(), "input error: f.size() != s.size()");
+	    // f: input format
+	    // s: input sizes
+	    SizeT j = 0;
+	    SizeT j0 = 0;
+	    typename FormatT::InputType nformat;
+	    auto npack = iter<0,NI>( [&](auto i) {
+		SizeT si = 1;
+		if(mIPack[i]->lmax().val() != 1){
+		    // CHECK!!!
+		    for(; si < mIPack[i]->lmax().val(); ++j){
+			si *= s[i];
+			CXZ_ASSERT(j < f.size(), "incompatible index formats");
+		    }
+		    CXZ_ASSERT(si == mIPack[i]->lmax().val(),
+			       "incompatible index formats: " << toString(s) << " vs " /*!!!*/);
+		    Vector<SizeT> nf(j-j0);
+		    Vector<SizeT> ns(j-j0);
+		    std::copy(f.begin()+j0,f.begin()+j,nf.begin());
+		    std::get<i>(nformat) = *std::min_element(nf.begin(), nf.end());
+		    std::for_each(nf.begin(), nf.end(), [&](SizeT& x)
+		    { CXZ_ASSERT(x % std::get<i>(nformat).val() == 0, "incompatible");
+			x /= std::get<i>(nformat).val(); } );
+		    std::copy(s.begin()+j0,s.begin()+j,ns.begin());
+		    mIPack[i]->reformat(nf,ns);
+		}
+	    }, NoF {});
+	    mFormat = FormatT(nformat);
+	    return *this;
+	}
     }
 
     template <class FormatT, class... Indices>
diff --git a/src/include/ranges/mrange.h b/src/include/ranges/mrange.h
index 4e960c2..2d9b1c0 100644
--- a/src/include/ranges/mrange.h
+++ b/src/include/ranges/mrange.h
@@ -94,7 +94,7 @@ namespace CNORXZ
 	auto deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
-	decltype(auto) reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
+	GMIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s);
 
 	GMIndex& setFormat(const FormatT& bs);
 
diff --git a/src/include/ranges/prange.cc.h b/src/include/ranges/prange.cc.h
index b5d82c9..ce687ee 100644
--- a/src/include/ranges/prange.cc.h
+++ b/src/include/ranges/prange.cc.h
@@ -174,13 +174,12 @@ namespace CNORXZ
     }
 
     template <class IndexT>
-    PIndex<IndexT> PIndex<IndexT>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    PIndex<IndexT>& PIndex<IndexT>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
-	CXZ_ASSERT(f.size() == 1, "expected format of dimension 1, got " << toString(f));
-	CXZ_ASSERT(s.size() == 1, "expected sizes of dimension 1, got " << toString(s));
-	CXZ_ASSERT(f[0] == 1, "trivial format ([1]), got " << toString(f));
-	CXZ_ASSERT(s[0] == lmax().val(), "expected size to be equal to index size (" << 
-		   lmax().val() << "), got " << s[0]);
+	CXZ_ASSERT(f[0]*s[0] == lmax().val(), "got wrong extension: " << f[0]*s[0]
+		   << " vs " << lmax().val());
+	CXZ_ASSERT(CNORXZ::formatIsTrivial(f,s), "format is not trivial: f = " << toString(f)
+		   << ", s = " << toString(s));
 	return *this;
     }
 
diff --git a/src/include/ranges/prange.h b/src/include/ranges/prange.h
index 1f25453..562a3e6 100644
--- a/src/include/ranges/prange.h
+++ b/src/include/ranges/prange.h
@@ -58,7 +58,7 @@ namespace CNORXZ
 	decltype(auto) deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
-	PIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
+	PIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s);
 
 	String stringMeta() const;
 	decltype(auto) meta() const;
diff --git a/src/include/ranges/srange.cc.h b/src/include/ranges/srange.cc.h
index a42918f..a5e9e55 100644
--- a/src/include/ranges/srange.cc.h
+++ b/src/include/ranges/srange.cc.h
@@ -184,7 +184,7 @@ namespace CNORXZ
     }
 
     template <typename MetaT, SizeT S>
-    SIndex<MetaT,S> SIndex<MetaT,S>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    SIndex<MetaT,S>& SIndex<MetaT,S>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
 	CXZ_ASSERT(f[0]*s[0] == lmax().val(), "got wrong extension: " << f[0]*s[0]
 		   << " vs " << lmax().val());
diff --git a/src/include/ranges/srange.h b/src/include/ranges/srange.h
index 34991f3..ea18367 100644
--- a/src/include/ranges/srange.h
+++ b/src/include/ranges/srange.h
@@ -64,7 +64,7 @@ namespace CNORXZ
 	SizeT deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
-	SIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
+	SIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s);
 
 	template <class Xpr, class F>
 	decltype(auto) ifor(const Xpr& xpr, F&& f) const;
diff --git a/src/include/ranges/urange.cc.h b/src/include/ranges/urange.cc.h
index c7bc3ad..52b5dce 100644
--- a/src/include/ranges/urange.cc.h
+++ b/src/include/ranges/urange.cc.h
@@ -170,7 +170,7 @@ namespace CNORXZ
     }
 
     template <typename MetaT>
-    UIndex<MetaT> UIndex<MetaT>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    UIndex<MetaT>& UIndex<MetaT>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
 	CXZ_ASSERT(f[0]*s[0] == lmax().val(), "got wrong extension: " << f[0]*s[0]
 		   << " vs " << lmax().val());
diff --git a/src/include/ranges/urange.h b/src/include/ranges/urange.h
index 9ddcbf4..8357503 100644
--- a/src/include/ranges/urange.h
+++ b/src/include/ranges/urange.h
@@ -70,7 +70,7 @@ namespace CNORXZ
 	SizeT deepMax() const;
 	
 	/** @copydoc IndexInterface::reformat() */
-	UIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
+	UIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s);
 
 	template <class Xpr, class F>
 	decltype(auto) ifor(const Xpr& xpr, F&& f) const;
diff --git a/src/include/ranges/xindex.cc.h b/src/include/ranges/xindex.cc.h
index 2f4537c..ff5db88 100644
--- a/src/include/ranges/xindex.cc.h
+++ b/src/include/ranges/xindex.cc.h
@@ -165,9 +165,10 @@ namespace CNORXZ
     }
 
     template <class Index, typename Meta>
-    XIndexPtr XIndex<Index,Meta>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    XIndex<Index,Meta>& XIndex<Index,Meta>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
-	return xindexPtr( moveToPtr( mI->reformat(f,s) ) );
+	mI->reformat(f,s);
+	return *this;
     }
 
     template <class Index, typename Meta>
diff --git a/src/include/ranges/xindex.h b/src/include/ranges/xindex.h
index 96b2ffe..bbb9411 100644
--- a/src/include/ranges/xindex.h
+++ b/src/include/ranges/xindex.h
@@ -53,7 +53,7 @@ namespace CNORXZ
 	virtual RangePtr prange(const XIndexPtr& last) const = 0;
 	virtual Vector<SizeT> deepFormat() const = 0;
 	virtual Vector<SizeT> deepMax() const = 0;
-	virtual XIndexPtr reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const = 0;
+	virtual XIndexBase& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) = 0;
 
 	virtual String stringMeta() const = 0;
 	virtual DType meta() const = 0;
@@ -107,7 +107,7 @@ namespace CNORXZ
 	virtual RangePtr prange(const XIndexPtr& last) const override final;
 	virtual Vector<SizeT> deepFormat() const override final;
 	virtual Vector<SizeT> deepMax() const override final;
-	virtual XIndexPtr reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const override final;
+	virtual XIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) override final;
 
 	virtual String stringMeta() const override final;
 	virtual DType meta() const override final;
diff --git a/src/include/ranges/yrange.h b/src/include/ranges/yrange.h
index f67d7a5..48febe8 100644
--- a/src/include/ranges/yrange.h
+++ b/src/include/ranges/yrange.h
@@ -80,7 +80,7 @@ namespace CNORXZ
 	const YFormat& format() const;
 	const YFormat& lexFormat() const;
 	YIndex& setFormat(const YFormat& bs);
-	YIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
+	YIndex& reformat(const Vector<SizeT>& f, const Vector<SizeT>& s);
 	
 	/** @copydoc IndexInterface::formatIsTrivial() */
 	bool formatIsTrivial() const;
diff --git a/src/lib/ranges/crange.cc b/src/lib/ranges/crange.cc
index a5674b0..cf6ec9e 100644
--- a/src/lib/ranges/crange.cc
+++ b/src/lib/ranges/crange.cc
@@ -144,7 +144,7 @@ namespace CNORXZ
 	return lmax().val();
     }
 
-    CIndex CIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    CIndex& CIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
 	CXZ_ASSERT(f[0]*s[0] == lmax().val(), "got wrong extension: " << f[0]*s[0]
 		   << " vs " << lmax().val());
diff --git a/src/lib/ranges/dindex.cc b/src/lib/ranges/dindex.cc
index c1f7235..c1dc73a 100644
--- a/src/lib/ranges/dindex.cc
+++ b/src/lib/ranges/dindex.cc
@@ -182,9 +182,10 @@ namespace CNORXZ
 	return mI->deepMax();
     }
 
-    DIndex DIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    DIndex& DIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
-	return DIndex(mI->reformat(f,s));
+	mI->reformat(f,s);
+	return *this;
     }
 
     bool DIndex::formatIsTrivial() const
diff --git a/src/lib/ranges/yrange.cc b/src/lib/ranges/yrange.cc
index 6a95961..10b3b8b 100644
--- a/src/lib/ranges/yrange.cc
+++ b/src/lib/ranges/yrange.cc
@@ -413,27 +413,25 @@ namespace CNORXZ
 	return o;
     }
 
-    YIndex YIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
+    YIndex& YIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s)
     {
 	CXZ_ASSERT(f.size() == s.size(), "input error: f.size() != s.size()");
 	// f: input format
 	// s: input sizes
 	SizeT j = 0;
 	SizeT j0 = 0;
-	Vector<UPos> nformat(dim());
-	Vector<XIndexPtr> npack(dim());
+	Vector<UPos> nformat;
 	for(SizeT i = 0; i != dim(); ++i){
 	    SizeT si = 1;
 	    if(mIs[i]->lmax().val() == 1){
-		npack[i] = mIs[i];
+		continue;
 	    }
 	    for(; si < mIs[i]->lmax().val(); ++j){
 		si *= s[i];
 		CXZ_ASSERT(j < f.size(), "incompatible index formats");
 	    }
 	    CXZ_ASSERT(si == mIs[i]->lmax().val(),
-		       "incompatible index formats: " << toString(s) << " vs " //!!!
-		       );
+		       "incompatible index formats: " << toString(s) << " vs " /*!!!*/);
 	    Vector<SizeT> nf(j-j0);
 	    Vector<SizeT> ns(j-j0);
 	    std::copy(f.begin()+j0,f.begin()+j,nf.begin());
@@ -441,11 +439,10 @@ namespace CNORXZ
 	    std::for_each(nf.begin(), nf.end(), [&](SizeT& x)
 	    { CXZ_ASSERT(x % nformat[i].val() == 0, "incompatible"); x /= nformat[i].val(); } );
 	    std::copy(s.begin()+j0,s.begin()+j,ns.begin());
-	    npack[i] = mIs[i]->reformat(nf,ns);
+	    mIs[i]->reformat(nf,ns);
 	}
-	YIndex oi ( YFormat(nformat), npack );
-	oi = lex();
-	return oi;
+	mFormat = YFormat(nformat);
+	return *this;
     }
 
     bool YIndex::formatIsTrivial() const