diff --git a/src/include/xpr/acc_xpr.cc.h b/src/include/xpr/acc_xpr.cc.h
new file mode 100644
index 0000000..901bde2
--- /dev/null
+++ b/src/include/xpr/acc_xpr.cc.h
@@ -0,0 +1,70 @@
+
+#ifndef __cxz_acc_xpr_cc_h__
+#define __cxz_acc_xpr_cc_h__
+
+#include "acc_xpr.h"
+
+namespace CNORXZ
+{
+    template <SizeT L, class Xpr, class F>
+    constexpr AccXpr<L,Xpr,F>::AccXpr(SizeT n, const IndexId<L>& id,
+				      const Xpr& xpr, F&& f) :
+	mN(n),
+	mId(id),
+	mXpr(xpr),
+	mExt(mXpr.rootSteps(mId)),
+	mF(std::forward<F>(f))
+    {}
+
+    template <SizeT L, class Xpr, class F>
+    template <class PosT>
+    inline decltype(auto) AccXpr<L,Xpr,F>::operator()(const PosT& last) const
+    {
+	if constexpr(std::is_same<typename std::remove_reference<F>::type,NoF>::value){
+	    const auto pos = last + mExt( UPos(mN) );
+	    mXpr(pos);
+	    return None {};
+	}
+	else {
+	    typedef typename
+		std::remove_reference<decltype(mXpr(last + mExt( UPos(0) )))>::type OutT;
+	    auto o = OutT();
+	    const auto pos = last + mExt( UPos(mN) );
+	    mF(o, mXpr(pos));
+	    return o;
+	}
+    }
+
+    template <SizeT L, class Xpr, class F>
+    inline decltype(auto) AccXpr<L,Xpr,F>::operator()() const
+    {
+	if constexpr(std::is_same<typename std::remove_reference<F>::type,NoF>::value){
+	    const auto pos = mExt( UPos(mN) );
+	    mXpr(pos);
+	    return None {};
+	}
+	else {
+	    typedef typename
+		std::remove_reference<decltype(mXpr( mExt( UPos(0) )))>::type OutT;
+	    auto o = OutT();
+	    const auto pos = mExt( UPos(mN) );
+	    mF(o, mXpr(pos));
+	    return o;
+	}
+    }
+
+    template <SizeT L, class Xpr, class F>
+    template <SizeT I>
+    inline decltype(auto) AccXpr<L,Xpr,F>::rootSteps(const IndexId<I>& id) const
+    {
+	return mXpr.rootSteps(id);
+    }
+
+    template <SizeT L, class Xpr, class F>
+    constexpr decltype(auto) accxpr(SizeT n, const IndexId<L>& id, const Xpr& xpr, F&& f)
+    {
+	return AccXpr<L,Xpr,F>(n, id, xpr, std::forward<F>(f));
+    }
+}
+
+#endif
diff --git a/src/include/xpr/acc_xpr.h b/src/include/xpr/acc_xpr.h
new file mode 100644
index 0000000..be41f67
--- /dev/null
+++ b/src/include/xpr/acc_xpr.h
@@ -0,0 +1,41 @@
+
+// rank access expression, fix rank position to current rank
+
+#ifndef __cxz_acc_xpr_h__
+#define __cxz_acc_xpr_h__
+
+//#include "base/base.h"
+#include "xpr_base.h"
+
+namespace CNORXZ
+{
+    template <SizeT L, class Xpr, class F = NoF>
+    class AccXpr : public XprInterface<AccXpr<L,Xpr,F>>
+    {
+    public:
+	DEFAULT_MEMBERS(AccXpr);
+
+	constexpr AccXpr(SizeT n, const IndexId<L>& id, const Xpr& xpr, F&& f);
+
+	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:
+	SizeT mN = 0;
+	IndexId<L> mId;
+	Xpr mXpr;
+	typedef decltype(mXpr.rootSteps(mId)) XPosT;
+	XPosT mExt;
+	F mF;
+    };
+
+    template <SizeT L, class Xpr, class F = NoF>
+    constexpr decltype(auto) accxpr(SizeT n, const IndexId<L>& id, const Xpr& xpr, F&& f);
+}
+
+#endif
diff --git a/src/include/xpr/racc_xpr.cc.h b/src/include/xpr/racc_xpr.cc.h
deleted file mode 100644
index 0326baf..0000000
--- a/src/include/xpr/racc_xpr.cc.h
+++ /dev/null
@@ -1,73 +0,0 @@
-
-#ifndef __cxz_racc_xpr_cc_h__
-#define __cxz_racc_xpr_cc_h__
-
-#include "racc_xpr.h"
-
-namespace CNOXRZ
-{
-    namespace mpi
-    {
-	template <SizeT L, class Xpr, class F = NoF>
-	constexpr AccXpr<L,Xpr,F>::AccXpr(SizeT n, const IndexId<L>& id,
-					  const Xpr& xpr, F&& f) :
-	    mN(n),
-	    mId(id),
-	    mXpr(xpr),
-	    mExt(mXpr.rootSteps(mId)),
-	    mF(std::forward<F>(f))
-	{}
-
-	template <SizeT L, class Xpr, class F = NoF>
-	template <class PosT>
-	inline decltype(auto) AccXpr<L,Xpr,F>::operator()(const PosT& last) const
-	{
-	    if constexpr(std::is_same<typename std::remove_reference<F>::type,NoF>::value){
-		const auto pos = last + mExt( UPos(mN) );
-		mXpr(pos);
-		return None {};
-	    }
-	    else {
-		typedef typename
-		    std::remove_reference<decltype(mXpr(last + mExt( UPos(0) )))>::type OutT;
-		auto o = OutT();
-		const auto pos = last + mExt( UPos(mN) );
-		mF(o, mXpr(pos));
-		return o;
-	    }
-	}
-
-	template <SizeT L, class Xpr, class F = NoF>
-	inline decltype(auto) AccXpr<L,Xpr,F>::operator()() const
-	{
-	    if constexpr(std::is_same<typename std::remove_reference<F>::type,NoF>::value){
-		const auto pos = mExt( UPos(mN) );
-		mXpr(pos);
-		return None {};
-	    }
-	    else {
-		typedef typename
-		    std::remove_reference<decltype(mXpr(last + mExt( UPos(0) )))>::type OutT;
-		auto o = OutT();
-		const auto pos = mExt( UPos(mN) );
-		mF(o, mXpr(pos));
-		return o;
-	    }
-	}
-
-	template <SizeT L, class Xpr, class F = NoF>
-	template <SizeT I>
-	inline decltype(auto) AccXpr<L,Xpr,F>::rootSteps(const IndexId<I>& id) const
-	{
-	    return mXpr.rootSteps(id);
-	}
-
-	template <SizeT L, class Xpr, class F = NoF>
-	constexpr decltype(auto) accxpr(SizeT n, const IndexId<L>& id, const Xpr& xpr, F&& f)
-	{
-	    return AccXpr<L,Xpr,F>(size, id, xpr, std::forward<F>(f));
-	}
-    }
-}
-
-#endif
diff --git a/src/include/xpr/racc_xpr.h b/src/include/xpr/racc_xpr.h
deleted file mode 100644
index 66ce09a..0000000
--- a/src/include/xpr/racc_xpr.h
+++ /dev/null
@@ -1,44 +0,0 @@
-
-// rank access expression, fix rank position to current rank
-
-#ifndef __cxz_racc_xpr_h__
-#define __cxz_racc_xpr_h__
-
-#include "mpi_base.h"
-
-namespace CNORXZ
-{
-    namespace mpi
-    {
-
-	template <SizeT L, class Xpr, class F = NoF>
-	class AccXpr : public XprInterface<AccXpr<L,Xpr,F>>
-	{
-	public:
-	    DEFAULT_MEMBERS(AccXpr);
-
-	    constexpr AccXpr(SizeT n, const IndexId<L>& id, const Xpr& xpr, F&& f);
-
-	    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:
-	    SizeT mN = 0;
-	    IndexId<L> mId;
-	    Xpr mXpr;
-	    typedef decltype(mXpr.rootSteps(mId)) XPosT;
-	    XPosT mExt;
-	    F mF;
-	};
-
-	template <SizeT L, class Xpr, class F = NoF>
-	constexpr decltype(auto) accxpr(SizeT n, const IndexId<L>& id, const Xpr& xpr, F&& f);
-    }
-}
-
-#endif
diff --git a/src/include/xpr/xpr.cc.h b/src/include/xpr/xpr.cc.h
index dab4606..1f57824 100644
--- a/src/include/xpr/xpr.cc.h
+++ b/src/include/xpr/xpr.cc.h
@@ -16,3 +16,4 @@
 #include "index_id.cc.h"
 #include "func.cc.h"
 #include "map_xpr.cc.h"
+#include "acc_xpr.cc.h"
diff --git a/src/include/xpr/xpr.h b/src/include/xpr/xpr.h
index e6fe804..b40dbeb 100644
--- a/src/include/xpr/xpr.h
+++ b/src/include/xpr/xpr.h
@@ -16,5 +16,6 @@
 #include "index_id.h"
 #include "func.h"
 #include "map_xpr.h"
+#include "acc_xpr.h"
 
 #include "xpr.cc.h"
diff --git a/src/opt/mpi/include/rarray.cc.h b/src/opt/mpi/include/rarray.cc.h
index dec610c..d64b306 100644
--- a/src/opt/mpi/include/rarray.cc.h
+++ b/src/opt/mpi/include/rarray.cc.h
@@ -169,6 +169,7 @@ namespace CNORXZ
 	inline decltype(auto) RCArray<T>::operator()(const DPack& pack) const
 	{
 	    // TODO: assert that none of the indices is rank index
+	    CXZ_ERROR("not implemented");
 	    return (*mA)(pack);
 	}
 
@@ -361,6 +362,7 @@ namespace CNORXZ
 	inline decltype(auto) RArray<T>::operator()(const DPack& pack) const
 	{
 	    // TODO: assert that none of the indices is rank index
+	    CXZ_ERROR("not implemented");
 	    return (*mB)(pack);
 	}
 
@@ -507,14 +509,13 @@ namespace CNORXZ
 	    }
 
 	    // Third loop: Assign map to target buffer positions:
-	    const SizeT myrankoff = myrank*locsz;
 	    assert(mapsize == Nranks*locsz);
 	    Vector<SizeT> cnt(Nranks);
 	    mi->ifor( operation
 		      ( [&](SizeT p) {
 			  const SizeT r = p / locsz;
 			  const SizeT l = p % locsz;
-			  const SizeT mpidx = (p - myrankoff + mapsize) % mapsize;
+			  const SizeT mpidx = p;
 			  if(myrank != r and required[p]){
 			      SizeT off = 0;
 			      for(SizeT s = 0; s != r; ++s){
@@ -524,7 +525,7 @@ namespace CNORXZ
 			      ++cnt[r];
 			  }
 			  if(myrank == r){
-			      assert(mpidx < locsz);
+			      assert(mpidx < (myrank+1)*locsz);
 			      map[mpidx] = data.data() + l*blocks;
 			  }
 		      } , posop(mi) ), NoF {} )();
diff --git a/src/opt/mpi/include/rmap_xpr.cc.h b/src/opt/mpi/include/rmap_xpr.cc.h
index 785db32..98e4715 100644
--- a/src/opt/mpi/include/rmap_xpr.cc.h
+++ b/src/opt/mpi/include/rmap_xpr.cc.h
@@ -23,23 +23,26 @@ namespace CNORXZ
 							const Sptr<SrcIndex>& si,
 							const F& f, const Sptr<Vector<SizeT>>& m)
     {
+	// This was the old shift, keep it here as comment if we want to introduce other shifts
+	// in order to reduce memory consumption by the maps;
+	// remember to invert the shift in the map xpr BEFORE calling the map!
+	//const SizeT locsz = tix.local()->pmax().val();
+	//const SizeT tarsize = locsz*mpi::getNumRanks();
+	//const SizeT idx = (tix.pos() - locsz*myrank + tarsize) % tarsize;
+
 	auto six = *si;
 	auto sie = si->range()->end();
 	auto tix = *ti;
-	const SizeT locsz = tix.local()->pmax().val();
-	const SizeT tarsize = locsz*mpi::getNumRanks();
 	const SizeT mapsize = m->size();
 	const SizeT myrank = mpi::getRankNumber();
 	if constexpr(mpi::is_rank_index<SrcIndex>::value){
-	    CXZ_ASSERT(mapsize == six.local()->pmax().val(), "map not well-formatted: size = "
+	    CXZ_ASSERT(mapsize == six.pmax().val(), "map not well-formatted: size = "
 		       << mapsize << ", expected " << six.local()->pmax().val());
 	    for(six = 0; six != sie; ++six){
 		tix.at( f(*six) );
 		if(six.rank() == myrank){
-		    //const SizeT idx = (tix.pos() - locsz*tix.rank() + tarsize) % tarsize;
-		    const SizeT idx = (tix.pos() - locsz*myrank + tarsize) % tarsize;
-		    //const SizeT idx = tix.pos();
-		    (*m)[six.local()->pos()] = idx;
+		    const SizeT idx = tix.pos();
+		    (*m)[six.pos()] = idx;
 		}
 	    }
 	}
@@ -48,9 +51,7 @@ namespace CNORXZ
 		       << mapsize << ", expected " << six.pmax().val());
 	    for(six = 0; six != sie; ++six){
 		tix.at( f(*six) );
-		//const SizeT idx = (tix.pos() - locsz*tix.rank() + tarsize) % tarsize;
-		const SizeT idx = (tix.pos() - locsz*myrank + tarsize) % tarsize;
-		//const SizeT idx = tix.pos()
+		const SizeT idx = tix.pos()
 		(*m)[six.pos()] = idx;
 	    }
 	}
@@ -62,13 +63,7 @@ namespace CNORXZ
 							const Sptr<SrcIndex>& si,
 							const F& f)
     {
-	SizeT mapsize = 0;
-	if constexpr(mpi::is_rank_index<SrcIndex>::value){
-	    mapsize = si->local()->lmax().val();
-	}
-	else {
-	    mapsize = si->lmax().val();
-	}
+	const SizeT mapsize = si->pmax().val();
 	auto o = std::make_shared<Vector<SizeT>>(mapsize);
 	setup(ti,si,f,o);
 	return o;
diff --git a/src/opt/mpi/include/rop_types.cc.h b/src/opt/mpi/include/rop_types.cc.h
index a1a3613..56010cb 100644
--- a/src/opt/mpi/include/rop_types.cc.h
+++ b/src/opt/mpi/include/rop_types.cc.h
@@ -29,12 +29,16 @@ namespace CNORXZ
 	template <class PosT>
 	constexpr decltype(auto) CROpRoot<T,RIndexT,IndexT>::operator()(const PosT& pos) const
 	{
+	    //CXZ_ASSERT(pos.val() < mRIndex->pmax().val(), pos.val() << ">=" << mRIndex->pmax().val());
+	    //CXZ_ASSERT(mData[pos.val()] != nullptr, "data[" << pos.val() << "] == null");
+	    //CXZ_ASSERT(pos.next().val() < mIndex->pmax().val(), pos.val() << ">=" << mIndex->pmax().val());
 	    return (mData[pos.val()])[pos.next().val()];
 	}
 
 	template <typename T, class RIndexT, class IndexT>
 	constexpr decltype(auto) CROpRoot<T,RIndexT,IndexT>::operator()() const
 	{
+	    //CXZ_ASSERT(mData[0] != nullptr, "data[" << 0 << "] == null");
 	    return (mData[0])[0];
 	}
 
@@ -61,11 +65,9 @@ namespace CNORXZ
 						     const Sptr<IndexT>& li) :
 	    mLocal(&a.local()),
 	    mData(a.buffermap().data()),
-	    //mData(a.data()),
 	    mRIndex(ri),
 	    mIndex(li)
 	{
-	    //CXZ_ERROR("nope");
 	    CXZ_ASSERT(a.buffermap().size() == ri->lmax().val(),
 		       "data map not properly initialized: map size = " << a.buffermap().size()
 		       << ", rank index range size = " << ri->lmax().val());
@@ -75,8 +77,8 @@ namespace CNORXZ
 	template <class Op>
 	constexpr ROpRoot<T,RIndexT,IndexT>& ROpRoot<T,RIndexT,IndexT>::operator=(const Op& in)
 	{
-	    (*mLocal)(mindexPtr(mRIndex->local()*mIndex)) = in;
-	    //OI::a(mIndex, [](auto& a, const auto& b) { a = b; }, in);
+	    (*mLocal)(mindexPtr(mRIndex->local()*mIndex)).a
+		(mindexPtr(mRIndex*mIndex),[](auto& a, const auto& b) { a = b; }, in);
 	    return *this;
 	}
 	
@@ -84,16 +86,16 @@ namespace CNORXZ
 	template <class Op>
 	constexpr ROpRoot<T,RIndexT,IndexT>& ROpRoot<T,RIndexT,IndexT>::operator+=(const Op& in)
 	{
-	    (*mLocal)(mindexPtr(mRIndex->local()*mIndex)) += in;
-	    //OI::a(mIndex, [](auto& a, const auto& b) { a += b; }, in);
+	    (*mLocal)(mindexPtr(mRIndex->local()*mIndex)).a
+		(mindexPtr(mRIndex*mIndex),[](auto& a, const auto& b) { a += b; }, in);
 	    return *this;
 	}
 	
 	template <typename T, class RIndexT, class IndexT>
 	constexpr ROpRoot<T,RIndexT,IndexT>& ROpRoot<T,RIndexT,IndexT>::operator=(const ROpRoot& in)
 	{
-	    (*mLocal)(mindexPtr(mRIndex->local()*mIndex)) = in;
-	    //OI::a(mIndex, [](auto& a, const auto& b) { a = b; }, in);
+	    (*mLocal)(mindexPtr(mRIndex->local()*mIndex)).a
+		(mindexPtr(mRIndex*mIndex),[](auto& a, const auto& b) { a = b; }, in);
 	    return *this;
 	}
 
@@ -101,12 +103,16 @@ namespace CNORXZ
 	template <class PosT>
 	constexpr decltype(auto) ROpRoot<T,RIndexT,IndexT>::operator()(const PosT& pos) const
 	{
+	    //CXZ_ASSERT(pos.val() < mRIndex->pmax().val(), pos.val() << ">=" << mRIndex->pmax().val());
+	    //CXZ_ASSERT(mData[pos.val()] != nullptr, "data[" << pos.val() << "] == null");
+	    //CXZ_ASSERT(pos.next().val() < mIndex->pmax().val(), pos.val() << ">=" << mIndex->pmax().val());
 	    return (mData[pos.val()])[pos.next().val()];
 	}
 
 	template <typename T, class RIndexT, class IndexT>
 	constexpr decltype(auto) ROpRoot<T,RIndexT,IndexT>::operator()() const
 	{
+	    //CXZ_ASSERT(mData[0] != nullptr, "data[" << 0 << "] == null");
 	    return (mData[0])[0];
 	}
 
diff --git a/src/opt/mpi/include/rop_types.h b/src/opt/mpi/include/rop_types.h
index 5415182..2c44259 100644
--- a/src/opt/mpi/include/rop_types.h
+++ b/src/opt/mpi/include/rop_types.h
@@ -116,6 +116,12 @@ namespace CNORXZ
 	static constexpr SizeT value = 2;
     };
     
+    template <typename T, class RIndexT, class IndexT>
+    struct op_size<mpi::ROpRoot<T,RIndexT,IndexT>>
+    {
+	static constexpr SizeT value = 2;
+    };
+    
 } // namespace CNORXZ
 
 #endif
diff --git a/src/opt/mpi/include/rrange.cc.h b/src/opt/mpi/include/rrange.cc.h
index d67af1f..de9c168 100644
--- a/src/opt/mpi/include/rrange.cc.h
+++ b/src/opt/mpi/include/rrange.cc.h
@@ -231,8 +231,7 @@ namespace CNORXZ
 		if constexpr(I != 0){ return SPos<0> {}; }
 		else { return UPos(id == this->id() ? 1 : 0); }
 	    };
-	    return mI->stepSize(id) + own();
-	    //return getRankStepSize(id);
+	    return mK->stepSize(id) * mI->pmax() * UPos(mRankFormat) + mI->stepSize(id) + own();
 	}
 
 	template <class IndexI, class IndexK>
@@ -330,7 +329,8 @@ namespace CNORXZ
 	template <class Xpr, class F>
 	constexpr decltype(auto) RIndex<IndexI,IndexK>::ifor(const Xpr& xpr, F&& f) const
 	{
-	    return mI->ifor(xpr, std::forward<F>(f));
+	    return accxpr( mpi::getRankNumber(), mK->id(), mI->ifor(xpr, std::forward<F>(f)),
+			   NoF {});
 	}
 
 	template <class IndexI, class IndexK>
diff --git a/src/opt/mpi/tests/roperation_unit_test.cc b/src/opt/mpi/tests/roperation_unit_test.cc
index 917758d..8c57ea0 100644
--- a/src/opt/mpi/tests/roperation_unit_test.cc
+++ b/src/opt/mpi/tests/roperation_unit_test.cc
@@ -138,11 +138,10 @@ namespace
 				   (std::get<2>(vec)+1)%L, (std::get<3>(vec)+1)%L); } );
 	Vector<bool> req(xp->range()->size(), false);
 	for(const auto& r: *imap1){
-	    req[(r+mpi::getRankNumber()*16*12*12*12/4)%req.size()] = true;
+	    req[r] = true;
 	}
 	res.load(x, AB, req); // DUMMY, not used...
 	mM1.load(xp, AB, req);
-	//res.rop(x*A*B) = mapXpr(xp,x,imap1, mM1(xp*A*B) - mM1(x*A*B) );
 	res(x*A*B) = mapXpr(xp,x,imap1, mM1(xp*A*B) - mM1(x*A*B) );
 
 	for(SizeT x0 = 0; x0 != T; ++x0) { 
diff --git a/src/opt/mpi/tests/setbuf_unit_test.cc b/src/opt/mpi/tests/setbuf_unit_test.cc
index 94be2a3..b977eb1 100644
--- a/src/opt/mpi/tests/setbuf_unit_test.cc
+++ b/src/opt/mpi/tests/setbuf_unit_test.cc
@@ -119,9 +119,9 @@ namespace
 	setupBuffer(rgi, req, data, buf, map, mSRange->size());
 
 	EXPECT_EQ(mRRange->sub(1)->size(), 16*12*12*12/4);
-	const SizeT locsz = rgj->local()->lmax().val();
-	const SizeT myrankoff = myrank*locsz;
-	const SizeT mapsize = map.size();
+	//const SizeT locsz = rgj->local()->lmax().val();
+	//const SizeT myrankoff = myrank*locsz;
+	//const SizeT mapsize = map.size();
 	// Fourth loop: Check:
 	for(*rgi = 0, gi = 0; rgi->lex() != rgi->lmax().val(); ++*rgi, ++gi){
 	    gj = gi.lex();
@@ -132,7 +132,8 @@ namespace
 	    *rgj = gj.lex();
 
 	    if(rgi->rank() == myrank){
-		const SizeT mpidx = (rgj->pos() - myrankoff + mapsize) % mapsize;
+		const SizeT mpidx = rgj->pos();
+		//const SizeT mpidx = (rgj->pos() - myrankoff + mapsize) % mapsize;
 		EXPECT_TRUE(map.data()[mpidx] != nullptr);
 		
 		const Double vn = *map[mpidx]/blocks;