diff --git a/fourindex.h b/fourindex.h
index cf14503..d1f88a3 100644
--- a/fourindex.h
+++ b/fourindex.h
@@ -1221,9 +1221,11 @@ protected:
 	unsigned int nnbas;
 friend class explicit_t2;
 public:
+	unsigned int nbas() const {return nnbas;};
         fourindex_dense(): NRSMat<T>() {nnbas=0;};
 	void resize(const int n) {nnbas=n; (*this).NRSMat<T>::resize(nnbas*nnbas);};
         explicit fourindex_dense(const int n): NRSMat<T>(n*n) {nnbas=n;};
+        explicit fourindex_dense(const int n, const NRSMat<T>&data): NRSMat<T>(data) {nnbas=n; if(data.nrows()!=n*n) laerror("data size mismatch in fourindex_dense antisymtwoelectronrealdiracAB constructor");};
 
 //here i,a are alpha j,b beta
         inline T& operator() (unsigned int i, unsigned int j, unsigned int a, unsigned int b)
@@ -1256,11 +1258,13 @@ return (*this).NRSMat<T>::operator() ((j-1)*nnbas+i-1,(b-1)*nnbas+a-1);
 template<class T, class I>
 class fourindex_dense<T2ijab_aces,T,I> : public NRMat<T> {
 protected:
-	unsigned int nocc,nvrt,ntri;
+	unsigned int ntri;
 friend class explicit_t2;
 public:
+	 unsigned int nocc,nvrt;
         fourindex_dense(): NRMat<T>() {nocc=nvrt=ntri=0;};
         explicit fourindex_dense(const int noc, const int nvr): NRMat<T>(noc*(noc-1)/2,nvr*(nvr-1)/2) {nocc=noc; nvrt=nvr; ntri=nvr*(nvr-1)/2;};
+        explicit fourindex_dense(const int noc, const int nvr, const NRMat<T> &data): NRMat<T>(data) {nocc=noc; nvrt=nvr; ntri=nvr*(nvr-1)/2; if(data.nrows()!=noc*(noc-1)/2 || data.ncols()!=nvr*(nvr-1)/2) laerror("data size mismatch in T2ijab_aces constructor"); };
 	void resize(const int noc, const int nvr) {(*this).NRMat<T>::resize(noc*(noc-1)/2,nvr*(nvr-1)/2); nocc=noc; nvrt=nvr; ntri=nvr*(nvr-1)/2;};
 
 //we cannot return reference due to the possible sign change
@@ -1322,8 +1326,10 @@ class fourindex_dense<antisymtwoelectronrealdirac,T,I> : public NRSMat<T> {
 private: 
 	int nnbas;
 public:
+	int nbas() const {return nnbas;};
 	fourindex_dense(): NRSMat<T>() {};
 	explicit fourindex_dense(const int n): nnbas(n), NRSMat<T>(n*(n-1)/2) {};
+	explicit fourindex_dense(const int n, const  NRSMat<T> &data): nnbas(n), NRSMat<T>(data) {if(data.nrows()!=n*(n-1)/2) laerror("data size mismatch in fourindex_dense antisymtwoelectronrealdirac constructor");};
 	fourindex_dense(const T &a, const int n): nnbas(n), NRSMat<T>(a,n*(n-1)/2) {};
 	fourindex_dense(const T *a, const int n): nnbas(n), NRSMat<T>(a,n*(n-1)/2) {};
 	//and also construct it from sparse and externally stored fourindex classes
diff --git a/t.cc b/t.cc
index 370e38f..0ae16fb 100644
--- a/t.cc
+++ b/t.cc
@@ -3743,9 +3743,8 @@ tensor2fourindex(t,ff);
 cout <<"Error = "<<(f-ff).norm()<<endl;
 }
 
-if(1)
+if(0)
 {
-//check also index order
 int n;
 cin>>n;
 fourindex_dense<T2IjAb_aces,double,int> f(n+1,n,n+3,n+2);
@@ -3757,7 +3756,49 @@ tensor2fourindex(t,ff);
 cout <<"Error = "<<(f-ff).norm()<<endl;
 }
 
+if(0)
+{
+int n;
+cin>>n;
+fourindex_dense<T2ijab_aces,double,int> f(n,n+2);
+f.randomize(1.);
+Tensor<double> t=fourindex2tensor(f);
+cout <<t;
+fourindex_dense<T2ijab_aces,double,int> ff;
+tensor2fourindex(t,ff);
+cout <<"Error = "<<(f-ff).norm()<<endl;
+}
 
+if(0)
+{
+int n;
+cin>>n;
+fourindex_dense<antisymtwoelectronrealdiracAB,double,int> f(n);
+f.randomize(1.);
+Tensor<double> t=fourindex2tensor(f);
+cout <<t;
+fourindex_dense<antisymtwoelectronrealdiracAB,double,int> ff;
+tensor2fourindex(t,ff);
+cout <<"Error = "<<(f-ff).norm()<<endl;
+}
+
+
+if(1)
+{
+int n;
+cin>>n;
+fourindex_dense<antisymtwoelectronrealdirac,double,int> f(n);
+f.randomize(1.);
+Tensor<double> t=fourindex2tensor(f);
+cout <<t;
+fourindex_dense<antisymtwoelectronrealdirac,double,int> ff;
+tensor2fourindex(t,ff);
+cout <<"Error = "<<(f-ff).norm()<<endl;
+}
+
+
+
+//@@@check operator() for all fourindex-tensor conversions
 
 
 }//main
diff --git a/tensor.h b/tensor.h
index 05ea12a..6683f3c 100644
--- a/tensor.h
+++ b/tensor.h
@@ -47,7 +47,7 @@
 //@@@ will not be particularly efficient
 //
 //@@@conversions to/from fourindex, optional negative range for beta spin handling in some cases
-//@@@use the fact that fourindex_dense is inherited from Mat/SMat and construct tensor from the (unsymmetrized) NRMat sharing data, just rewrite then the shape
+//@@@check operator() for all fourindex-tensor conversions
 //
 //@@@?general permutation of individual indices - check the indices in sym groups remain adjacent, calculate result's shape, loopover the result and permute using unwind_callback
 //
@@ -414,6 +414,109 @@ f=fourindex_dense<T2IjAb_aces,T,I>(noca,nocb,nvra,nvrb,mat);
 
 
 
+template<typename T, typename I>
+Tensor<T>  fourindex2tensor(const fourindex_dense<T2ijab_aces,T,I> &f)
+{
+NRVec<indexgroup> shape(2);
+for(int i=0; i<2; ++i)
+	{
+	shape[i].number=2;
+	shape[i].symmetry= -1;
+	shape[i].offset=1;
+	}
+shape[1].range=f.nocc;
+shape[0].range=f.nvrt;
+NRVec<T> data(f);
+return Tensor<T>(shape,data);
+}
+
+template<typename T, typename I>
+void tensor2fourindex(const Tensor<T> &t, fourindex_dense<T2ijab_aces,T,I> &f)
+{
+if(t.rank()!=4) laerror("wrong rank in tensor2fourindex");
+if(t.shape.size()!=2) laerror("wrong symmetry groups in tensor2fourindex");
+int nvrt=t.shape[0].range;
+int nocc=t.shape[1].range;
+int offset=t.shape[0].offset;
+for(int i=0; i<t.shape.size(); ++i)
+	{
+	if(offset!=t.shape[i].offset) laerror("offset mismatch in tensor2fourindex");
+	if(-1!=t.shape[i].symmetry) laerror("symmetry mismatch in tensor2fourindex");
+	}
+NRMat<T> mat(t.data,nocc*(nocc-1)/2,nvrt*(nvrt-1)/2);
+f=fourindex_dense<T2ijab_aces,T,I>(nocc,nvrt,mat);
+}
+
+
+
+template<typename T, typename I>
+Tensor<T>  fourindex2tensor(const fourindex_dense<antisymtwoelectronrealdiracAB,T,I> &f)
+{
+NRVec<indexgroup> shape(4);
+int n=f.nbas();
+for(int i=0; i<4; ++i)
+	{
+	shape[i].number=1;
+	shape[i].symmetry=0;
+	shape[i].offset=1;
+	shape[i].range=n;
+	}
+NRMat<T> data(f); //expand to full matrix
+return Tensor<T>(shape,NRVec<T>(data));
+}
+
+template<typename T, typename I>
+void tensor2fourindex(const Tensor<T> &t, fourindex_dense<antisymtwoelectronrealdiracAB,T,I> &f)
+{
+if(t.rank()!=4) laerror("wrong rank in tensor2fourindex");
+if(t.shape.size()!=4) laerror("wrong symmetry groups in tensor2fourindex");
+int range=t.shape[0].range;
+int offset=t.shape[0].offset;
+for(int i=0; i<t.shape.size(); ++i)
+	{
+	if(range!=t.shape[i].range) laerror("range mismatch in tensor2fourindex");
+	if(offset!=t.shape[i].offset) laerror("offset mismatch in tensor2fourindex");
+	if(0!=t.shape[i].symmetry) laerror("symmetry mismatch in tensor2fourindex");
+	}
+NRMat<T> mat(t.data,range*range,range*range);
+f=fourindex_dense<antisymtwoelectronrealdiracAB,T,I>(range,NRSMat<T>(mat));
+}
+
+
+
+template<typename T, typename I>
+Tensor<T>  fourindex2tensor(const fourindex_dense<antisymtwoelectronrealdirac,T,I> &f)
+{
+NRVec<indexgroup> shape(2);
+int n=f.nbas();
+for(int i=0; i<2; ++i)
+	{
+	shape[i].number=2;
+	shape[i].symmetry= -1;
+	shape[i].offset=1;
+	shape[i].range=n;
+	}
+NRMat<T> mat(f);
+NRVec<T> data(mat); //expand symmetric to full matrix for index group symmetry
+return Tensor<T>(shape,data);
+}
+
+template<typename T, typename I>
+void tensor2fourindex(const Tensor<T> &t, fourindex_dense<antisymtwoelectronrealdirac,T,I> &f)
+{
+if(t.rank()!=4) laerror("wrong rank in tensor2fourindex");
+if(t.shape.size()!=2) laerror("wrong symmetry groups in tensor2fourindex");
+int range=t.shape[0].range;
+int offset=t.shape[0].offset;
+for(int i=0; i<t.shape.size(); ++i)
+	{
+	if(range!=t.shape[i].range) laerror("range mismatch in tensor2fourindex");
+	if(offset!=t.shape[i].offset) laerror("offset mismatch in tensor2fourindex");
+	if(-1!=t.shape[i].symmetry) laerror("symmetry mismatch in tensor2fourindex");
+	}
+NRMat<T> mat(t.data,range*(range-1)/2,range*(range-1)/2);
+f=fourindex_dense<antisymtwoelectronrealdirac,T,I>(range,NRSMat<T>(mat)); //symmetrize mat 
+}