diff --git a/src/include/array/array_base.cc.h b/src/include/array/array_base.cc.h
index da94e41..ae1218f 100644
--- a/src/include/array/array_base.cc.h
+++ b/src/include/array/array_base.cc.h
@@ -130,10 +130,20 @@ namespace CNORXZ
 	}
 	else {
 	    if(i->formatIsTrivial()){
-		// try to apply container format
-		auto aformat = begin().deepFormat();
-		CXZ_ERROR("IMPLEMENT " << toString(aformat));
-		return coproot(*this, i);
+		// try to apply container format.
+		// if the reformat changes the index type in any manner
+		// the format is not applicable:
+		if constexpr(std::is_same<decltype(i->reformat( Vector<SizeT>(), Vector<SizeT>() )),Index>::value){
+		    auto beg = begin();
+		    auto aformat = beg.deepFormat();
+		    auto amax = beg.deepMax();
+		    auto fi = i->reformat( aformat, amax );
+		    return coproot(*this, moveToPtr( fi ) );
+		}
+		else {
+		    this->checkFormatCompatibility(*i);
+		    return coproot(*this, i);
+		}
 	    }
 	    else {
 		// check if format is compatible
@@ -313,10 +323,20 @@ namespace CNORXZ
 	}
 	else {
 	    if(i->formatIsTrivial()){
-		// try to apply container format
-		auto aformat = begin().deepFormat();
-		CXZ_ERROR("IMPLEMENT " << toString(aformat));
-		return oproot(*this, i);
+		// try to apply container format.
+		// if the reformat changes the index type in any manner
+		// the format is not applicable:
+		if constexpr(std::is_same<decltype(i->reformat( Vector<SizeT>(), Vector<SizeT>() )),Index>::value){
+		    auto beg = begin();
+		    auto aformat = beg.deepFormat();
+		    auto amax = beg.deepMax();
+		    auto fi = i->reformat( aformat, amax );
+		    return oproot(*this, moveToPtr( fi ) );
+		}
+		else {
+		    this->checkFormatCompatibility(*i);
+		    return oproot(*this, i);
+		}
 	    }
 	    else {
 		// check if format is compatible
diff --git a/src/include/ranges/crange.h b/src/include/ranges/crange.h
index 8937d8c..707b796 100644
--- a/src/include/ranges/crange.h
+++ b/src/include/ranges/crange.h
@@ -107,6 +107,9 @@ namespace CNORXZ
 	/** @copydoc IndexInterface::deepFormat() */
 	SizeT deepFormat() const;
 
+	/** @copydoc IndexInterface::deepMax() */
+	SizeT deepMax() const;
+
 	/** @copydoc IndexInterface::reformat() */
 	CIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
 	
diff --git a/src/include/ranges/dindex.h b/src/include/ranges/dindex.h
index 340a8eb..d0402d1 100644
--- a/src/include/ranges/dindex.h
+++ b/src/include/ranges/dindex.h
@@ -64,6 +64,7 @@ namespace CNORXZ
 	DIndex& at(const DType& meta);
 	RangePtr prange(const DIndex& end) const;
 	Vector<SizeT> deepFormat() const;
+	Vector<SizeT> deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
 	DIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
diff --git a/src/include/ranges/index_base.h b/src/include/ranges/index_base.h
index 4b371f7..14e0c2e 100644
--- a/src/include/ranges/index_base.h
+++ b/src/include/ranges/index_base.h
@@ -173,9 +173,13 @@ namespace CNORXZ
 	/** recursive index format */
 	decltype(auto) deepFormat() const { return THIS().deepFormat(); }
 
-	/** reformat index, return new index instance
+	/** max of all single-indices (recursive) */
+	decltype(auto) deepMax() const { return THIS().deepMax(); }
+	
+	/** 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); }
 	
diff --git a/src/include/ranges/mrange.cc.h b/src/include/ranges/mrange.cc.h
index 08e7021..457cec1 100644
--- a/src/include/ranges/mrange.cc.h
+++ b/src/include/ranges/mrange.cc.h
@@ -462,7 +462,7 @@ namespace CNORXZ
 		return false;
 	    }
 	    const bool ret2 = iter<0,NI-1>
-		( [&](auto j) { return mFormat[CSizeT<j>{}].val() == mIPack[CSizeT<j+1>{}].lmax().val() * mFormat[CSizeT<j+1>{}].val(); },
+		( [&](auto j) { return mFormat[CSizeT<j>{}].val() == mIPack[CSizeT<j+1>{}]->lmax().val() * mFormat[CSizeT<j+1>{}].val(); },
 		  [](const auto&... x) { return (x and ...); });
 	    if(ret2 and mFormat[CSizeT<NI-1>{}].val() == 1){
 		return true;
@@ -512,7 +512,7 @@ namespace CNORXZ
     }
 
     template <class FormatT, class... Indices>
-    RangePtr GMIndex<FormatT,Indices...>::prange(const MIndex<Indices...>& last) const
+    RangePtr GMIndex<FormatT,Indices...>::prange(const GMIndex<FormatT,Indices...>& last) const
     {
 	return iter<0,NI>
 	    ( [&](auto i) {
@@ -531,6 +531,13 @@ namespace CNORXZ
 			   [&](const auto&... e) { return concat(e...); } );
     }
 
+    template <class FormatT, class... Indices>
+    auto GMIndex<FormatT,Indices...>::deepMax() const
+    {
+	return iter<0,NI>( [&](auto i) { return mIPack[i]->deepMax(); },
+			   [&](const auto&... e) { return concat(e...); } );
+    }
+
     template <class FormatT, class... Indices>
     decltype(auto)
     GMIndex<FormatT,Indices...>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
@@ -563,7 +570,7 @@ namespace CNORXZ
 	    { CXZ_ASSERT(x % nformat[i].val() == 0, "incompatible"); x /= nformat[i].val(); } );
 	    std::copy(s.begin()+j0,s.begin()+j,ns.begin());
 	    return moveToPtr( mIPack[i]->reformat(nf,ns) );
-	}, [](auto&... e) { return std::make_tuple( e... ); } );
+	}, [](const auto&... e) { return std::make_tuple( e... ); } );
 	GMIndex<MFormat<NI>,Indices...> oi { MFormat<NI>(nformat),SPack<Indices...>(npack) };
 	oi = lex();
 	return oi;
diff --git a/src/include/ranges/mrange.h b/src/include/ranges/mrange.h
index ccdc64e..4e960c2 100644
--- a/src/include/ranges/mrange.h
+++ b/src/include/ranges/mrange.h
@@ -89,8 +89,9 @@ namespace CNORXZ
 	const SPack<Indices...>& pack() const;
 	const auto& format() const;
 	const auto& lexFormat() const;
-	RangePtr prange(const MIndex<Indices...>& last) const;
+	RangePtr prange(const GMIndex<FormatT,Indices...>& last) const;
 	auto deepFormat() const;
+	auto deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
 	decltype(auto) reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
@@ -248,6 +249,7 @@ namespace CNORXZ
     {
 	static constexpr bool value = (index_expression_exists<Indices>::value and ...);
     };
+
 }
 
 #endif
diff --git a/src/include/ranges/prange.cc.h b/src/include/ranges/prange.cc.h
index b4128e4..b5d82c9 100644
--- a/src/include/ranges/prange.cc.h
+++ b/src/include/ranges/prange.cc.h
@@ -167,6 +167,12 @@ namespace CNORXZ
 	return mOrig->deepFormat();
     }
 
+    template <class IndexT>
+    decltype(auto) PIndex<IndexT>::deepMax() const
+    {
+	return mOrig->deepMax();
+    }
+
     template <class IndexT>
     PIndex<IndexT> PIndex<IndexT>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
     {
diff --git a/src/include/ranges/prange.h b/src/include/ranges/prange.h
index 729ded2..1f25453 100644
--- a/src/include/ranges/prange.h
+++ b/src/include/ranges/prange.h
@@ -55,6 +55,7 @@ namespace CNORXZ
 	UPos stepSize(const IndexId<I>& id) const;
 	RangePtr prange(const PIndex<IndexT>& last) const;
 	decltype(auto) deepFormat() const;
+	decltype(auto) deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
 	PIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
diff --git a/src/include/ranges/srange.cc.h b/src/include/ranges/srange.cc.h
index c8add42..9c26769 100644
--- a/src/include/ranges/srange.cc.h
+++ b/src/include/ranges/srange.cc.h
@@ -177,6 +177,12 @@ namespace CNORXZ
 	return 1;
     }
 
+    template <typename MetaT, SizeT S>
+    SizeT SIndex<MetaT,S>::deepMax() const
+    {
+	return lmax().val();
+    }
+
     template <typename MetaT, SizeT S>
     SIndex<MetaT,S> SIndex<MetaT,S>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
     {
diff --git a/src/include/ranges/srange.h b/src/include/ranges/srange.h
index 3b8b560..34991f3 100644
--- a/src/include/ranges/srange.h
+++ b/src/include/ranges/srange.h
@@ -61,6 +61,7 @@ namespace CNORXZ
 
 	RangePtr prange(const SIndex<MetaType,S>& last) const;
 	SizeT deepFormat() const;
+	SizeT deepMax() const;
 
 	/** @copydoc IndexInterface::reformat() */
 	SIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
diff --git a/src/include/ranges/urange.cc.h b/src/include/ranges/urange.cc.h
index 9131ebd..68bea1c 100644
--- a/src/include/ranges/urange.cc.h
+++ b/src/include/ranges/urange.cc.h
@@ -163,14 +163,25 @@ namespace CNORXZ
 	return 1;
     }
 
+    template <typename MetaT>
+    SizeT UIndex<MetaT>::deepMax() const
+    {
+	return lmax().val();
+    }
+
     template <typename MetaT>
     UIndex<MetaT> UIndex<MetaT>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
     {
+	// can also get multi dim stuff, but:
+	// * overall extension must match
+	// * f must be trivial
+	/*
 	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]);
+	*/
 	return *this;
     }
 
diff --git a/src/include/ranges/urange.h b/src/include/ranges/urange.h
index 534b2d9..9ddcbf4 100644
--- a/src/include/ranges/urange.h
+++ b/src/include/ranges/urange.h
@@ -67,6 +67,8 @@ namespace CNORXZ
 
 	SizeT deepFormat() const;
 
+	SizeT deepMax() const;
+	
 	/** @copydoc IndexInterface::reformat() */
 	UIndex reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const;
 
diff --git a/src/include/ranges/xindex.cc.h b/src/include/ranges/xindex.cc.h
index 5754c32..2f4537c 100644
--- a/src/include/ranges/xindex.cc.h
+++ b/src/include/ranges/xindex.cc.h
@@ -158,6 +158,12 @@ namespace CNORXZ
 	return toVec( mI->deepFormat() );
     }
     
+    template <class Index, typename Meta>
+    Vector<SizeT> XIndex<Index,Meta>::deepMax() const
+    {
+	return toVec( mI->deepMax() );
+    }
+
     template <class Index, typename Meta>
     XIndexPtr XIndex<Index,Meta>::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
     {
diff --git a/src/include/ranges/xindex.h b/src/include/ranges/xindex.h
index 4dce7bf..96b2ffe 100644
--- a/src/include/ranges/xindex.h
+++ b/src/include/ranges/xindex.h
@@ -52,6 +52,7 @@ namespace CNORXZ
 	virtual UPos stepSize(const IndexId<0>& id) const = 0;
 	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 String stringMeta() const = 0;
@@ -105,6 +106,7 @@ namespace CNORXZ
 	virtual UPos stepSize(const IndexId<0>& id) const override final;
 	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 String stringMeta() const override final;
diff --git a/src/include/ranges/yrange.h b/src/include/ranges/yrange.h
index 547aa04..444b225 100644
--- a/src/include/ranges/yrange.h
+++ b/src/include/ranges/yrange.h
@@ -76,6 +76,7 @@ namespace CNORXZ
 	const DPack& pack() const;
 	RangePtr prange(const YIndex& last) const;
 	Vector<SizeT> deepFormat() const;
+	Vector<SizeT> deepMax() const;
 	const YFormat& format() const;
 	const YFormat& lexFormat() const;
 	YIndex& setFormat(const YFormat& bs);
diff --git a/src/lib/ranges/crange.cc b/src/lib/ranges/crange.cc
index 159c30f..b19dd2e 100644
--- a/src/lib/ranges/crange.cc
+++ b/src/lib/ranges/crange.cc
@@ -139,6 +139,11 @@ namespace CNORXZ
 	return 1;
     }
 
+    SizeT CIndex::deepMax() const
+    {
+	return lmax().val();
+    }
+
     CIndex CIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
     {
 	CXZ_ASSERT(f.size() == 1, "expected format of dimension 1, got " << toString(f));
diff --git a/src/lib/ranges/dindex.cc b/src/lib/ranges/dindex.cc
index 4c7e066..c1f7235 100644
--- a/src/lib/ranges/dindex.cc
+++ b/src/lib/ranges/dindex.cc
@@ -177,6 +177,11 @@ namespace CNORXZ
 	return mI->deepFormat();
     }
 
+    Vector<SizeT> DIndex::deepMax() const
+    {
+	return mI->deepMax();
+    }
+
     DIndex DIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
     {
 	return DIndex(mI->reformat(f,s));
diff --git a/src/lib/ranges/yrange.cc b/src/lib/ranges/yrange.cc
index 41067a6..6a95961 100644
--- a/src/lib/ranges/yrange.cc
+++ b/src/lib/ranges/yrange.cc
@@ -395,6 +395,23 @@ namespace CNORXZ
 	}
 	return o;
     }
+    
+    Vector<SizeT> YIndex::deepMax() const
+    {
+	Vector<Vector<SizeT>> dmv(mIs.size());
+	SizeT osize = 0;
+	for(SizeT j = 0; j != dmv.size(); ++j){
+	    dmv[j] = mIs[j]->deepMax();
+	    osize += dmv[j].size();
+	}
+	Vector<SizeT> o(osize);
+	SizeT off = 0;
+	for(SizeT j = 0; j != dmv.size(); ++j){
+	    std::copy(dmv[j].begin(), dmv[j].end(), o.begin()+off);
+	    off += dmv[j].size();
+	}
+	return o;
+    }
 
     YIndex YIndex::reformat(const Vector<SizeT>& f, const Vector<SizeT>& s) const
     {