diff --git a/t.cc b/t.cc
index e99d72e..fa24f7a 100644
--- a/t.cc
+++ b/t.cc
@@ -3200,7 +3200,7 @@ cout <<d;
 }
 
 
-if(1)
+if(0)
 {
 INDEXGROUP g;
 g.number=3;
@@ -3243,4 +3243,32 @@ cout <<epsilon.data;
 cout <<epsilon;
 }
 
+if(1)
+{
+int n=3;
+NRVec<INDEXGROUP> s(4);
+for(int i=0; i<4; ++i) 
+	{
+	s[i].number=1;
+	s[i].symmetry=0;
+	s[i].offset=0;
+	s[i].range=n;
+	}
+Tensor<double> t(s);
+t.randomize(1.);
+cout <<t;
+NRPerm<int> p({3,1,4,2});
+Tensor<double> tt=t.permute_index_groups(p);
+cout <<tt;
+for(int i=0; i<n; ++i)
+	for(int j=0; j<n; ++j)
+		for(int k=0; k<n; ++k)
+			for(int l=0; l<n; ++l)
+				{
+				if(t(i,j,k,l)!=tt(k,i,l,j)) laerror("error in permute_index_groups");
+				}
+}
+
+
+
 }
diff --git a/tensor.cc b/tensor.cc
index 227400f..7b9d44c 100644
--- a/tensor.cc
+++ b/tensor.cc
@@ -27,13 +27,14 @@
 namespace LA {
 
 template<typename T>
-int Tensor<T>:: calcrank()  
+int Tensor<T>:: calcrank()
 {
 int r=0;
 for(int i=0; i<shape.size(); ++i)
         {
-        if(shape[i].number==0) laerror("empty index group");
-        r+=shape[i].number;
+	const indexgroup *sh = &(* const_cast<const NRVec<indexgroup> *>(&shape))[i];
+        if(sh->number==0) laerror("empty index group");
+        r+=sh->number;
         }
 myrank=r;
 return r;
@@ -49,19 +50,20 @@ cumsizes.resize(shape.size());
 LA_largeindex s=1;
 for(int i=0; i<shape.size(); ++i)
         {
-        if(shape[i].number==0) laerror("empty index group");
-        if(shape[i].range==0) return 0;
+	const indexgroup *sh = &(* const_cast<const NRVec<indexgroup> *>(&shape))[i];
+        if(sh->number==0) laerror("empty index group");
+        if(sh->range==0) return 0;
         cumsizes[i]=s;
-        switch(shape[i].symmetry)
+        switch(sh->symmetry)
                 {
                 case 0:
-                        s *= groupsizes[i] = longpow(shape[i].range,shape[i].number);
+                        s *= groupsizes[i] = longpow(sh->range,sh->number);
                         break;
                 case 1:
-                        s *= groupsizes[i] = simplicial(shape[i].number,shape[i].range);
+                        s *= groupsizes[i] = simplicial(sh->number,sh->range);
                         break;
                 case -1:
-                        s *= groupsizes[i] = simplicial(shape[i].number,shape[i].range-shape[i].number+1);
+                        s *= groupsizes[i] = simplicial(sh->number,sh->range-sh->number+1);
                         break;
                 default: 
                         laerror("illegal index group symmetry");
@@ -376,20 +378,21 @@ template<typename T>
 void loopingroups(Tensor<T> &t, int ngroup, int igroup, T **p, SUPERINDEX &I, void (*callback)(const SUPERINDEX &, T *))
 {
 LA_index istart,iend;
-switch(t.shape[ngroup].symmetry)
+const indexgroup *sh = &(* const_cast<const NRVec<indexgroup> *>(&t.shape))[ngroup];
+switch(sh->symmetry)
 	{
 	case 0:
-		istart= t.shape[ngroup].offset;
-		iend=   t.shape[ngroup].offset+t.shape[ngroup].range-1;
+		istart= sh->offset;
+		iend=   sh->offset+sh->range-1;
 		break;
 	case 1:
-		istart= t.shape[ngroup].offset;
-		if(igroup==t.shape[ngroup].number-1) iend=   t.shape[ngroup].offset+t.shape[ngroup].range-1;
+		istart= sh->offset;
+		if(igroup==sh->number-1) iend=   sh->offset+sh->range-1;
 		else iend = I[ngroup][igroup+1];
 		break;
 	case -1:
-		istart= t.shape[ngroup].offset + igroup;
-		if(igroup==t.shape[ngroup].number-1) iend=   t.shape[ngroup].offset+t.shape[ngroup].range-1;
+		istart= sh->offset + igroup;
+		if(igroup==sh->number-1) iend=   sh->offset+sh->range-1;
                 else iend = I[ngroup][igroup+1]-1;
 		break;
 	}
@@ -410,7 +413,8 @@ for(LA_index i = istart; i<=iend; ++i)
 		if(newigroup<0)
 			{
 			--newngroup;
-			newigroup=t.shape[newngroup].number-1;
+			const indexgroup *sh2 = &(* const_cast<const NRVec<indexgroup> *>(&t.shape))[newngroup];
+			newigroup=sh2->number-1;
 			}
 		loopingroups(t,newngroup,newigroup,p,I,callback);
 		}
@@ -422,9 +426,16 @@ template<typename T>
 void Tensor<T>::loopover(void (*callback)(const SUPERINDEX &, T *))
 {
 SUPERINDEX I(shape.size());
-for(int i=0; i<I.size(); ++i) {I[i].resize(shape[i].number); I[i] = shape[i].offset;}
+for(int i=0; i<I.size(); ++i)
+	{
+	const indexgroup *sh = &(* const_cast<const NRVec<indexgroup> *>(&shape))[i];
+	I[i].resize(sh->number); 
+	I[i] = sh->offset;
+	}
 T *pp=&data[0];
-loopingroups(*this,shape.size()-1,shape[shape.size()-1].number-1,&pp,I,callback);
+int ss=shape.size()-1;
+const indexgroup *sh = &(* const_cast<const NRVec<indexgroup> *>(&shape))[ss];
+loopingroups(*this,ss,sh->number-1,&pp,I,callback);
 }
 
 
@@ -487,6 +498,60 @@ return s;
 
 
 
+template<typename T>
+void loopovergroups(Tensor<T> &t, int ngroup, T **p, GROUPINDEX &I, void (*callback)(const GROUPINDEX &, T *))
+{
+for(LA_largeindex i = 0; i<t.groupsizes[ngroup]; ++i)
+	{
+	I[ngroup]=i;
+	if(ngroup==0) (*callback)(I,(*p)++);
+	else loopovergroups(t,ngroup-1,p,I,callback);
+	}
+}
+
+template<typename T>
+void Tensor<T>::grouploopover(void (*callback)(const GROUPINDEX &, T *))
+{
+GROUPINDEX I(shape.size());
+T *pp=&data[0];
+loopovergroups(*this,shape.size()-1,&pp,I,callback);
+}
+
+
+const NRPerm<int> *help_p;
+template<typename T> 
+Tensor<T> *help_t;
+
+template<typename T>
+static void permutecallback(const GROUPINDEX &I, T *v)
+{
+LA_largeindex target=0;
+for(int i=0; i< help_t<T>->shape.size(); ++i)
+	{
+	target += I[(*help_p)[i+1]-1] * help_t<T>->cumsizes[i];
+	}
+help_t<T>->data[target] = *v;
+}
+
+
+
+template<typename T>
+Tensor<T> Tensor<T>::permute_index_groups(const NRPerm<int> &p) const
+{
+NRVec<indexgroup> newshape=shape.permuted(p);
+Tensor<T> r(newshape);
+
+//prepare statics for the callback
+help_p = &p;
+help_t<T> = &r;
+
+//now rearrange the data
+const_cast<Tensor<T> *>(this)->grouploopover(permutecallback<T>);
+return r;
+}
+
+
+
 template class Tensor<double>;
 template class Tensor<std::complex<double> >;
 template std::ostream & operator<<(std::ostream &s, const Tensor<double> &x);
diff --git a/tensor.h b/tensor.h
index 884b0a7..12cd254 100644
--- a/tensor.h
+++ b/tensor.h
@@ -97,6 +97,7 @@ class LA_traits<indexgroup> {
 
 typedef NRVec<LA_index> FLATINDEX; //all indices but in a single vector
 typedef NRVec<NRVec<LA_index> > SUPERINDEX; //all indices in the INDEXGROUP structure
+typedef NRVec<LA_largeindex> GROUPINDEX; //set of indices in the symmetry groups
 
 
 template<typename T>
@@ -104,10 +105,9 @@ class Tensor {
 public:
 	NRVec<indexgroup> shape;
 	NRVec<T> data;	
-private:
 	int myrank;
 	NRVec<LA_largeindex> groupsizes; //group sizes of symmetry index groups (a function of shape but precomputed for efficiency)
-	NRVec<LA_largeindex> cumsizes; //cumulative sizes of symmetry index groups (a function of shape but precomputed for efficiency)
+	NRVec<LA_largeindex> cumsizes; //cumulative sizes of symmetry index groups (a function of shape but precomputed for efficiency); always cumsizes[0]=1, index group 0 is the innermost-loop one
 
 public:
 	LA_largeindex index(int *sign, const SUPERINDEX &I) const; //map the tensor indices to the position in data
@@ -117,7 +117,7 @@ public:
 
 	//constructors
 	Tensor() : myrank(0) {};
-	Tensor(const NRVec<indexgroup> &s) : shape(s), data((int)calcsize()) {calcrank();}; //general tensor
+	Tensor(const NRVec<indexgroup> &s) : shape(s) { data.resize(calcsize()); calcrank();}; //general tensor
 	Tensor(const indexgroup &g) {shape.resize(1); shape[0]=g; data.resize(calcsize()); calcrank();}; //tensor with a single index group
 	Tensor(const Tensor &rhs): myrank(rhs.myrank), shape(rhs.shape), groupsizes(rhs.groupsizes), cumsizes(rhs.cumsizes), data(rhs.data) {};
 	Tensor(int xrank, const NRVec<indexgroup> &xshape, const NRVec<LA_largeindex> &xgroupsizes,  const  NRVec<LA_largeindex> xcumsizes, const  NRVec<T> &xdata) :  myrank(xrank), shape(xshape), groupsizes(xgroupsizes), cumsizes(xcumsizes), data(xdata) {};
@@ -173,14 +173,17 @@ public:
 
 	inline void randomize(const typename LA_traits<T>::normtype &x) {data.randomize(x);};
 
-	void loopover(void (*callback)(const SUPERINDEX &, T *));
+	void loopover(void (*callback)(const SUPERINDEX &, T *)); //loop over all elements
+	void grouploopover(void (*callback)(const GROUPINDEX &, T *)); //loop over all elements disregarding the internal structure of index groups
+
+	Tensor permute_index_groups(const NRPerm<int> &p) const; //rearrange the tensor storage permuting index groups as a whole
 
 	//@@@TODO - unwinding to full size in a specified index
 	//@@@contraction by a whole index group or by individual single index
+	//@@@ general antisymmetrization operator Kucharski style
 	//@@@TODO - contractions - basic and efficient? first contraction in a single index; between a given group+index in group at each tensor
 	//@@@outer product and product with a contraction
 	//@@@@symmetrize a group, antisymmetrize a group, expand a (anti)symmetric grtoup - obecne symmetry change krome +1 na -1 vse mozne
-	//@@@@@@permute index groups
 };