diff --git a/triqs/arrays/indexmaps/range.hpp b/triqs/arrays/indexmaps/range.hpp
index 43ef283f..c02cb98d 100644
--- a/triqs/arrays/indexmaps/range.hpp
+++ b/triqs/arrays/indexmaps/range.hpp
@@ -40,6 +40,8 @@ namespace arrays {
   range(std::ptrdiff_t first__, std::ptrdiff_t last__, std::ptrdiff_t step__ = 1)
      : first_(first__), last_(last__), step_(step__) {}
 
+  range(std::ptrdiff_t i) : range (i,i+1,1){}
+  
   std::ptrdiff_t first() const { return first_; }
   std::ptrdiff_t last() const { return last_; }
   std::ptrdiff_t step() const { return step_; }
diff --git a/triqs/gfs/block.hpp b/triqs/gfs/block.hpp
index ce0d6598..cd4ab913 100644
--- a/triqs/gfs/block.hpp
+++ b/triqs/gfs/block.hpp
@@ -97,13 +97,13 @@ namespace gfs {
  block_gf<Variable, Target, Opt> make_block_gf(int n, gf<Variable, Target, Opt> const &g) {
   auto V = std::vector<gf<Variable, Target, Opt>>{};
   for (int i = 0; i < n; ++i) V.push_back(g);
-  return {{n}, std::move(V), nothing{}, nothing{}};
+  return {{n}, std::move(V), nothing{}, nothing{}, nothing{}};
  }
 
  // from a vector of gf (moving directly)
  template <typename Variable, typename Target, typename Opt>
  block_gf<Variable, Target, Opt> make_block_gf(std::vector<gf<Variable, Target, Opt>> V) {
-  return {{int(V.size())}, std::move(V), nothing{}, nothing{}};
+  return {{int(V.size())}, std::move(V), nothing{}, nothing{}, nothing{}};
  }
 
  // from a vector of gf : generalized to have a different type of gf in the vector (e.g. views...)
@@ -111,13 +111,13 @@ namespace gfs {
  block_gf<Variable, Target, Opt> make_block_gf(std::vector<GF2> const &V) {
   auto V2 = std::vector<gf<Variable, Target, Opt>>{};
   for (auto const &g : V) V2.push_back(g);
-  return {{int(V.size())}, std::move(V2), nothing{}, nothing{}};
+  return {{int(V.size())}, std::move(V2), nothing{}, nothing{}, nothing{}};
  }
 
  // from a init list of GF with the correct type
  template <typename Variable, typename Target, typename Opt>
  block_gf<Variable, Target, Opt> make_block_gf(std::initializer_list<gf<Variable, Target, Opt>> const &V) {
-  return {{int(V.size())}, V, nothing{}, nothing{}};
+  return {{int(V.size())}, V, nothing{}, nothing{}, nothing{}};
  }
 
  // from vector<string> and a gf to be copied
@@ -125,7 +125,7 @@ namespace gfs {
  block_gf<Variable, Target, Opt> make_block_gf(std::vector<std::string> block_names, gf<Variable, Target, Opt> const &g) {
   auto V = std::vector<gf<Variable, Target, Opt>>{};
   for (int i = 0; i < block_names.size(); ++i) V.push_back(g);
-  return {{block_names}, std::move(V), nothing{}, nothing{}};
+  return {{block_names}, std::move(V), nothing{}, nothing{}, nothing{}};
  }
 
  // from vector<string>, vector<gf>
@@ -133,7 +133,7 @@ namespace gfs {
  block_gf<Variable, Target, Opt> make_block_gf(std::vector<std::string> block_names, std::vector<gf<Variable, Target, Opt>> V) {
   if (block_names.size() != V.size())
    TRIQS_RUNTIME_ERROR << "make_block_gf(vector<string>, vector<gf>) : the two vectors do not have the same size !";
-  return {{block_names}, std::move(V), nothing{}, nothing{}};
+  return {{block_names}, std::move(V), nothing{}, nothing{}, nothing{}};
  }
 
  // from vector<string>, init_list<GF>
@@ -141,7 +141,7 @@ namespace gfs {
  block_gf<Variable, Target, Opt> make_block_gf(std::vector<std::string> block_names,
                                                std::initializer_list<gf<Variable, Target, Opt>> const &V) {
   if (block_names.size() != V.size()) TRIQS_RUNTIME_ERROR << "make_block_gf(vector<string>, init_list) : size mismatch !";
-  return {{block_names}, V, nothing{}, nothing{}};
+  return {{block_names}, V, nothing{}, nothing{}, nothing{}};
  }
 
  // -------------------------------   Free Factories for view type  --------------------------------------------------
@@ -149,17 +149,17 @@ namespace gfs {
  template <typename G0, typename... G>
  gf_view<block_index, typename std::remove_reference<G0>::type::view_type> make_block_gf_view(G0 &&g0, G &&... g) {
   auto V = std::vector<typename std::remove_reference<G0>::type::view_type>{std::forward<G0>(g0), std::forward<G>(g)...};
-  return {{int(V.size())}, std::move(V), nothing{}, nothing{}};
+  return {{int(V.size())}, std::move(V), nothing{}, nothing{}, nothing{}};
   // return { gf_mesh<block_index, Opt> {int(V.size())}, std::move(V), nothing{}, nothing{} } ;
  }
 
  template <typename GF> gf_view<block_index, typename GF::regular_type> make_block_gf_view_from_vector(std::vector<GF> V) {
-  return {{int(V.size())}, std::move(V), nothing{}, nothing{}};
+  return {{int(V.size())}, std::move(V), nothing{}, nothing{}, nothing{}};
  }
 
  // for cython proxy only. do not document.
  template <typename GF, typename GF2> gf_view<block_index, GF> make_block_gf_view_from_vector_of_cython_proxy(std::vector<GF2> V) {
-  return {{int(V.size())}, std::move(V), nothing{}, nothing{}};
+  return {{int(V.size())}, std::move(V), nothing{}, nothing{}, nothing{}};
  }
 
  // ------------------------------- Extend reinterpret_scalar_valued_gf_as_matrix_valued for block gf   ------
diff --git a/triqs/gfs/gf.hpp b/triqs/gfs/gf.hpp
index 554b5a9c..e134086b 100644
--- a/triqs/gfs/gf.hpp
+++ b/triqs/gfs/gf.hpp
@@ -72,6 +72,15 @@ namespace gfs {
    using type = nothing;
   };
 
+  // indices 
+  template <typename Target, typename Opt> struct indices {
+   using type = nothing;
+  };
+
+  template <typename Opt> struct indices<matrix_valued, Opt> {
+   using type = indices_2;
+  };
+
   // data_proxy contains function to manipulate the data array, but no data itself.
   // this is used to specialize this part of the code to array of dim 3 (matrix gf), dim 1 (scalar gf) and vector (e.g. block gf,
   // ...)
@@ -119,6 +128,7 @@ namespace gfs {
   using mesh_point_t = typename mesh_t::mesh_point_t;
   using mesh_index_t = typename mesh_t::index_t;
   using symmetry_t = typename gfs_implementation::symmetry<Variable, Target, Opt>::type;
+  using indices_t = typename gfs_implementation::indices<Target, Opt>::type;
   using evaluator_t = gfs_implementation::evaluator<Variable, Target, Opt>;
 
   using data_proxy_t = gfs_implementation::data_proxy<Variable, Target, Opt>;
@@ -138,6 +148,7 @@ namespace gfs {
   singularity_t &singularity() { return _singularity; }
   singularity_t const &singularity() const { return _singularity; }
   symmetry_t const &symmetry() const { return _symmetry; }
+  indices_t const &indices() const { return _indices; }
   evaluator_t const &get_evaluator() const { return _evaluator; }
 
   auto get_data_shape() const DECL_AND_RETURN(get_shape(this -> data()));
@@ -147,6 +158,10 @@ namespace gfs {
   data_t _data;
   singularity_t _singularity;
   symmetry_t _symmetry;
+  indices_t _indices;
+  public : 
+  std::string name;
+  protected : 
   evaluator_t _evaluator;
   data_proxy_t _data_proxy;
 
@@ -160,6 +175,8 @@ namespace gfs {
        _data(factory<data_t>(x.data())),
        _singularity(factory<singularity_t>(x.singularity())),
        _symmetry(x.symmetry()),
+       _indices(x.indices()),
+       name(x.name),
        _evaluator(x._evaluator) {}
 
   gf_impl(gf_impl &&) = default;
@@ -171,15 +188,21 @@ namespace gfs {
         _data(factory<data_t>(x.data())),
         _singularity(factory<singularity_t>(x.singularity())),
         _symmetry(x.symmetry()),
+        _indices(x.indices()),
+        name(x.name),
         _evaluator(x.get_evaluator()) {}
 
   template <typename M, typename D, typename S, typename SY, typename EV>
-  gf_impl(M &&m, D &&dat, S &&sing, SY &&sy, EV &&ev)
-     : _mesh(std::forward<M>(m)),
-       _data(std::forward<D>(dat)),
-       _singularity(std::forward<S>(sing)),
-       _symmetry(std::forward<SY>(sy)),
-       _evaluator(std::forward<EV>(ev)) {}
+  gf_impl(M &&m, D &&dat, S &&sing, SY &&sy, indices_t ind, std::string name, EV &&ev)
+     : _mesh(std::forward<M>(m))
+     , _data(std::forward<D>(dat))
+     , _singularity(std::forward<S>(sing))
+     , _symmetry(std::forward<SY>(sy))
+     , _indices(std::move(ind))
+     , name(name)
+     , _evaluator(std::forward<EV>(ev)) {
+   if (!_indices.check_size(this)) TRIQS_RUNTIME_ERROR << "Size of indices mismatch with data size";
+  }
 
   void operator=(gf_impl const &rhs) = delete; // done in derived class.
 
@@ -189,6 +212,8 @@ namespace gfs {
    swap(this->_data, b._data);
    swap(this->_singularity, b._singularity);
    swap(this->_symmetry, b._symmetry);
+   swap(this->_indices, b._indices);
+   swap(this->name, b.name);
    swap(this->_evaluator, b._evaluator);
   }
 
@@ -320,6 +345,8 @@ namespace gfs {
    ar &TRIQS_MAKE_NVP("singularity", _singularity);
    ar &TRIQS_MAKE_NVP("mesh", _mesh);
    ar &TRIQS_MAKE_NVP("symmetry", _symmetry);
+   ar &TRIQS_MAKE_NVP("indices", _indices);
+   ar &TRIQS_MAKE_NVP("name", name);
   }
 
   /// print
@@ -391,17 +418,19 @@ namespace gfs {
    *this = x;
   }
 
-  gf(typename B::mesh_t m, typename B::data_t dat, typename B::singularity_view_t const &si, typename B::symmetry_t const &s)
-     : B(std::move(m), std::move(dat), si, s, typename B::evaluator_t{}) {}
+  gf(typename B::mesh_t m, typename B::data_t dat, typename B::singularity_view_t const &si, typename B::symmetry_t const &s,
+     typename B::indices_t const &ind, std::string name = "")
+     : B(std::move(m), std::move(dat), si, s, ind, name, typename B::evaluator_t{}) {}
 
   using target_shape_t = typename factory::target_shape_t;
 
-  gf(typename B::mesh_t m, target_shape_t shape = target_shape_t{})
-     : B(std::move(m), factory::make_data(m, shape), factory::make_singularity(m, shape), typename B::symmetry_t{},
+  gf(typename B::mesh_t m, target_shape_t shape = target_shape_t{}, typename B::indices_t const &ind = typename B::indices_t{})
+     : B(std::move(m), factory::make_data(m, shape), factory::make_singularity(m, shape), typename B::symmetry_t{}, ind, {}, // clean unncessary types
          typename B::evaluator_t{}) {}
 
   friend void swap(gf &a, gf &b) noexcept { a.swap_impl(b); }
 
+  // CLEAN THIS : one op only gf rhs, + move 
   gf &operator=(gf const &rhs) {
    *this = gf(rhs);
    return *this;
@@ -424,6 +453,7 @@ namespace gfs {
    this->_singularity = rhs.singularity();
    // to be implemented : there is none in the gf_expr in particular....
    // this->_symmetry = rhs.symmetry();
+   // indices and name are not affected by it ???
   }
  };
 
@@ -454,14 +484,17 @@ namespace gfs {
   gf_view(gf_impl<Variable, Target, Opt, false, false> &&g) noexcept : B(std::move(g), bool {}) {} // from a gf &&
 
   template <typename D>
-  gf_view(typename B::mesh_t const &m, D const &dat, typename B::singularity_view_t const &t, typename B::symmetry_t const &s)
-     : B(m, factory<typename B::data_t>(dat), t, s, typename B::evaluator_t{}) {}
+  gf_view(typename B::mesh_t const &m, D const &dat, typename B::singularity_view_t const &t, typename B::symmetry_t const &s,
+          typename B::indices_t const &ind, std::string name = "")
+     : B(m, factory<typename B::data_t>(dat), t, s, ind, name, typename B::evaluator_t{}) {}
 
   void rebind(gf_view const &X) noexcept {
    this->_mesh = X._mesh;
    this->_symmetry = X._symmetry;
    this->_data_proxy.rebind(this->_data, X);
    this->_singularity.rebind(X._singularity);
+   this->_indices = X._indices;
+   this->name = X.name;
   }
 
   void rebind(gf_view<Variable, Target, Opt, false> const &X) noexcept {
@@ -489,8 +522,9 @@ namespace gfs {
   gf_view(gf_impl<Variable, Target, Opt, false, false> &&g) noexcept : B(std::move(g), bool {}) {} // from a gf &&
 
   template <typename D>
-  gf_view(typename B::mesh_t const &m, D const &dat, typename B::singularity_view_t const &t, typename B::symmetry_t const &s)
-     : B(m, factory<typename B::data_t>(dat), t, s, typename B::evaluator_t{}) {}
+  gf_view(typename B::mesh_t const &m, D const &dat, typename B::singularity_view_t const &t, typename B::symmetry_t const &s,
+          typename B::indices_t const &ind = typename B::indices_t{}, std::string name = "")
+    : B(m, factory<typename B::data_t>(dat), t, s, ind, name, typename B::evaluator_t{}) {}
 
   friend void swap(gf_view &a, gf_view &b) noexcept { a.swap_impl(b); }
 
@@ -499,6 +533,8 @@ namespace gfs {
    this->_symmetry = X._symmetry;
    this->_data_proxy.rebind(this->_data, X);
    this->_singularity.rebind(X._singularity);
+   this->_indices = X._indices;
+   this->name = X.name;
   }
 
   gf_view &operator=(gf_view const &rhs) {
@@ -540,7 +576,7 @@ namespace gfs {
   static_assert(std::is_same<Target, matrix_valued>::value, "slice_target only for matrix_valued GF's");
   using arrays::range;
   return {g.mesh(),                                                   g.data()(range(), std::forward<Args>(args)...),
-          slice_target(g.singularity(), std::forward<Args>(args)...), g.symmetry()};
+          slice_target(g.singularity(), std::forward<Args>(args)...), g.symmetry(), slice(g.indices(),std::forward<Args>(args)...), g.name };
  }
 
  template <typename Variable, typename Target, typename Opt, typename... Args>
@@ -560,7 +596,7 @@ namespace gfs {
   static_assert(std::is_same<Target, matrix_valued>::value, "slice_target only for matrix_valued GF's");
   using arrays::range;
   return {g.mesh(),                                                g.data()(range(), std::forward<Args>(args)...),
-          slice_target(g.singularity(), range(args, args + 1)...), g.symmetry()};
+          slice_target(g.singularity(), range(args, args + 1)...), g.symmetry(), {}, g.name};
  }
 
  template <typename Variable, typename Target, typename Opt, typename... Args>
@@ -573,6 +609,15 @@ namespace gfs {
   return slice_target_to_scalar(g(), std::forward<Args>(args)...);
  }
 
+ /*// slice with string arguments, for python mainly.
+ template <typename Variable, typename Target, typename Opt>
+ gf_view<Variable, matrix_valued, Opt> slice_target_string_indices(gf_view<Variable, Target, Opt> g, std::string const & a1, std::string const & a2) {
+  int n1 = g.indices().convert_index(a1,0);
+  int n2 = g.indices().convert_index(a2,1);
+  return slice_target (g, n1, n2); // the slice will have no indices. Ok ?
+ }
+*/
+
  // ---------------------------------- target reinterpretation ------------------------------------
  
  // a scalar_valued gf can be viewed as a 1x1 matrix
@@ -581,7 +626,7 @@ namespace gfs {
  reinterpret_scalar_valued_gf_as_matrix_valued(gf_view<Variable, scalar_valued, Opt, IsConst> g) {
   using a_t = typename gf_view<Variable, matrix_valued, Opt, IsConst>::data_view_t;
   auto a = a_t{typename a_t::indexmap_type(join(g.data().shape(), make_shape(1, 1))), g.data().storage()};
-  return {g.mesh(), a, g.singularity(), g.symmetry()};
+  return {g.mesh(), a, g.singularity(), g.symmetry(), {} , g.name};
  }
 
  template <typename Variable, typename Opt>
@@ -677,6 +722,8 @@ namespace gfs {
     h5_write(gr, "singularity", g._singularity);
     h5_write(gr, "mesh", g._mesh);
     h5_write(gr, "symmetry", g._symmetry);
+    h5_write(gr, "indices", g._indices);
+    //h5_write(gr, "name", g.name);
    }
 
    template <bool B> static void read(h5::group gr, gf_impl<Variable, Target, Opt, B, false> &g) {
@@ -684,6 +731,8 @@ namespace gfs {
     h5_read(gr, "singularity", g._singularity);
     h5_read(gr, "mesh", g._mesh);
     h5_read(gr, "symmetry", g._symmetry);
+    h5_read(gr, "indices", g._indices);
+    //h5_read(gr, "name", g.name);
    }
   };
  } // gfs_implementation
diff --git a/triqs/gfs/local/no_tail.hpp b/triqs/gfs/local/no_tail.hpp
index 80be390d..6b38cc05 100644
--- a/triqs/gfs/local/no_tail.hpp
+++ b/triqs/gfs/local/no_tail.hpp
@@ -30,7 +30,7 @@ namespace gfs {
 
  template <typename Variable, typename Target, bool V, bool C>
  gf_view<Variable, Target, no_tail, C> make_gf_view_without_tail(gf_impl<Variable, Target, void, V, C> const &g) {
-  return {g.mesh(), g.data(), {}, g.symmetry()};
+  return {g.mesh(), g.data(), {}, g.symmetry(), g.indices(), g.name};
  }
 
  namespace details { // dispatch the test for scalar_valued and matrix_valued
diff --git a/triqs/gfs/tools.hpp b/triqs/gfs/tools.hpp
index 3b7294ac..9a0276b9 100644
--- a/triqs/gfs/tools.hpp
+++ b/triqs/gfs/tools.hpp
@@ -74,6 +74,73 @@ namespace gfs {
  template <typename... T> closest_pt_wrap<T...> closest_mesh_pt(T &&... x) {
   return closest_pt_wrap<T...>{std::forward<T>(x)...};
  }
+ //------------------------------------------------------
+
+ // A simple indice struct
+ // Replace empty state by optional ?
+ struct indices_2 {
+
+  std::vector<std::vector<std::string>> ind;
+
+  indices_2() = default;
+  indices_2(std::vector<std::vector<std::string>> _ind) : ind(std::move(_ind)) {}
+
+  bool is_empty() const { return ind.size() == 0; }
+
+  template <typename G> bool check_size(G *g) const {
+   return (is_empty() ||
+           ((ind.size() == 2) && (ind[0].size() == get_target_shape(*g)[0]) && (ind[1].size() == get_target_shape(*g)[1])));
+  }
+
+  std::vector<std::string> operator[](int i) const {
+   if (is_empty())
+    return {};
+   else
+    return ind[i];
+  }
+
+  arrays::range convert_index(std::string const &s, int l_r) const {
+   if (!is_empty()) {
+    auto b = ind[l_r].begin(), e = ind[l_r].end();
+    auto it = std::find(b, e, s);
+    if (it != e) return it - b;
+   }
+   TRIQS_RUNTIME_ERROR << "There are no string indices for this Green function";
+  }
+
+  friend class boost::serialization::access;
+  template <class Archive> void serialize(Archive &ar, const unsigned int version) { ar &TRIQS_MAKE_NVP("ind", ind); }
+
+  friend void h5_write(h5::group fg, std::string subgroup_name, indices_2 const &g) {
+   if (g.is_empty()) return;
+   auto gr = fg.create_group(subgroup_name);
+   h5_write(gr, "left", g.ind[0]);
+   h5_write(gr, "right", g.ind[1]);
+  }
+
+  friend void h5_read(h5::group fg, std::string subgroup_name, indices_2 &g) {
+   h5::group gr;
+   try {
+    gr = fg.open_group(subgroup_name);
+   }
+   catch (...) {
+    g = indices_2{}; // empty, no file
+    return;
+   }
+   h5_read(gr, "left", g.ind[0]);
+   h5_read(gr, "right", g.ind[1]);
+  }
+ };
+
+ // inline indices_2 slice(indices_2 const & ind, arrays::range rl, arrays::range rr) {
+ // return {};
+ // }
+
+ inline indices_2 slice(indices_2 const &ind, arrays::range rl, arrays::range rr) {
+  if (ind.is_empty()) return {};
+  return {}; // MODIFY : slice the indices !!!
+  TRIQS_RUNTIME_ERROR << "Not implemented : slice of string indices";
+ }
 
  //------------------------------------------------------
 
@@ -87,10 +154,12 @@ namespace gfs {
   template <typename RHS> void operator=(RHS &&) {}
   friend void h5_write(h5::group, std::string subgroup_name, nothing) {}
   friend void h5_read(h5::group, std::string subgroup_name, nothing) {}
+  template <typename... A> friend nothing slice(nothing, A...) { return nothing(); }
   friend class boost::serialization::access;
   template <class Archive> void serialize(Archive &ar, const unsigned int version) {}
   friend nothing operator+(nothing, nothing) { return nothing(); }
   template <typename RHS> friend void assign_from_expression(nothing &, RHS) {}
+  template<typename A> bool check_size(A) {return true;}
  };
 
  template <typename... T> nothing slice_target(nothing, T...) { return nothing(); }