diff --git a/test/triqs/gfs/g_k_om2.cpp b/test/triqs/gfs/g_k_om2.cpp
index f6589a8f..2139b3ff 100644
--- a/test/triqs/gfs/g_k_om2.cpp
+++ b/test/triqs/gfs/g_k_om2.cpp
@@ -2,16 +2,20 @@
 #include <triqs/gfs.hpp>
 #include <triqs/gfs/bz.hpp>
 
+
+// FAIRE make_value !!
+//
 using namespace triqs::gfs;
 using namespace triqs::clef;
 using namespace triqs::arrays;
 using namespace triqs::lattice;
 template <typename Function, typename Mesh>
 // requires ( is_function_on_mesh<Function,Mesh>())
-auto  sum(Function const &f, Mesh const &m)->decltype(f(typename Mesh::mesh_point_t{})) {
+auto  sum(Function const &f, Mesh const &m) ->decltype(make_matrix(0*f(*(m.begin())))) {
  //auto sum(Function const &f, Mesh const &m) {
- auto res = decltype(f(typename Mesh::mesh_point_t{})) {};
- for (auto const &x : m)  res = res + f(x);
+ //auto res = typename triqs::regular_type_if_exists_else_type<decltype(f(typename Mesh::mesh_point_t{}))>::type (f(m.begin()));
+ auto res = make_matrix(0*f(*(m.begin())));
+ for (auto const &x : m) res = res + f(x);
  return res;
 }
 namespace triqs {
@@ -21,7 +25,7 @@ namespace triqs {
  }
 }
 
-#define TEST(X) std::cout << BOOST_PP_STRINGIZE((X)) << " ---> " << (X) << std::endl << std::endl;
+#define TEST(...) std::cout << BOOST_PP_STRINGIZE((__VA_ARGS__)) << " ---> " << (__VA_ARGS__) << std::endl << std::endl;
 
 int main() {
  try {
@@ -41,16 +45,25 @@ int main() {
   G_k_iom(k_, w_) << 1 / (w_ - eps(k_));
 
 
-  auto G_loc = gf<imfreq>{{beta,Fermion, 100}};
-  //G_loc(w_) << sum(k_ >> G_k_iom(k_,w_), g_eps.mesh());//does not compile
+  auto G_loc = gf<imfreq, matrix_valued, no_tail>{{beta, Fermion, 100}, {1, 1}};
+
+  auto r = G_k_iom(k_t{0, 0}, matsubara_freq{0, beta, Fermion});
+
+  auto r5 = sum(k_ >> G_k_iom(k_,0), g_eps.mesh());
+  G_loc(w_) << sum(k_ >> G_k_iom(k_,w_), g_eps.mesh());
 
   TEST(G_loc(0));
 
   auto G_k_tau = gf<cartesian_product<bz, imtime>>{{{bz_, 20}, {beta, Fermion, 100}}, {1, 1}};
   
- //curry<1>(G_k_tau) [k_] << inverse_fourier(curry<1>(G_k_iom)[k_]); //does not compile
+  //auto r3 = partial_eval<0>(G_k_iom,0);
+  //auto r4 = partial_eval<0>(G_k_tau,0);
+  //auto gt = curry<0>(G_k_tau) [0];
+  //auto  gw = curry<0>(G_k_iom)[0];
+ 
+  //curry<0>(G_k_tau) [k_] << inverse_fourier(curry<0>(G_k_iom)[k_]); 
   
-  //TEST(G_k_tau(0,0));
+  //TEST(G_k_tau[{0,0}]);
 
   // hdf5 
   //H5::H5File file("ess_g_k_om.h5", H5F_ACC_TRUNC );
diff --git a/triqs/clef/clef.hpp b/triqs/clef/clef.hpp
index e299e0c5..ff512ac5 100644
--- a/triqs/clef/clef.hpp
+++ b/triqs/clef/clef.hpp
@@ -170,8 +170,7 @@ namespace triqs { namespace clef {
   };                                                                                                                             \
  }                                                                                                                               \
  template <typename L, typename R>                                                                                               \
- typename std::enable_if<is_any_lazy<L, R>::value, expr<tags::TAG, expr_storage_t<L>, expr_storage_t<R>>>::type operator OP(     \
-     L&& l, R&& r) {                                                                                                             \
+ std14::enable_if_t<is_any_lazy<L, R>::value, expr<tags::TAG, expr_storage_t<L>, expr_storage_t<R>>> operator OP(L&& l, R&& r) { \
   return {tags::TAG(), std::forward<L>(l), std::forward<R>(r)};                                                                  \
  }                                                                                                                               \
  template <> struct operation<tags::TAG> {                                                                                       \
@@ -198,7 +197,7 @@ namespace triqs { namespace clef {
   };                                                                                                                             \
  }                                                                                                                               \
  template <typename L>                                                                                                           \
- typename std::enable_if<is_any_lazy<L>::value, expr<tags::TAG, expr_storage_t<L>>>::type operator OP(L&& l) {                   \
+ std14::enable_if_t<is_any_lazy<L>::value, expr<tags::TAG, expr_storage_t<L>>> operator OP(L&& l) {                   \
   return {tags::TAG(), std::forward<L>(l)};                                                                                      \
  }                                                                                                                               \
  template <> struct operation<tags::TAG> {                                                                                       \
@@ -223,11 +222,7 @@ namespace triqs { namespace clef {
  /* ---------------------------------------------------------------------------------------------------
   * Evaluation of the expression tree.
   *  --------------------------------------------------------------------------------------------------- */
- //template<typename ... T> struct _or; 
- //template<typename T0, typename ... T> struct _or<T0,T...> : std::integral_constant<bool,T0::value || _or<T...>::value>{}; 
- //template<> struct _or<> : std::false_type{};
 
- // just to try
  constexpr bool __or() { return false;}
  template<typename  ... B> constexpr bool __or(bool b, B... bs) { return b || __or(bs...); }
 
@@ -283,8 +278,8 @@ namespace triqs { namespace clef {
   static constexpr bool is_lazy = __or(evaluator<Childs, Pairs...>::is_lazy...);
 
   auto operator()(expr<Tag, Childs...> const& ex, Pairs const&... pairs) const {
-   auto eval_in_context = [&pairs](auto const& _child) { return eval(_child, pairs); };
-   return triqs::tuple::apply_compose(op_dispatch<Tag, is_lazy>{}, eval_in_context, ex.childs);
+   auto eval_in_context = [&pairs...](auto const& _child) { return eval(_child, pairs...); };
+   return tuple::apply_compose(op_dispatch<Tag, is_lazy>{}, eval_in_context, ex.childs);
   }
  };
 #else
@@ -299,8 +294,10 @@ namespace triqs { namespace clef {
 
  template <typename Tag, typename... Childs, typename... Pairs> struct evaluator_node_gal<2, expr<Tag, Childs...>, Pairs...> {
   static constexpr bool is_lazy = __or(evaluator<Childs, Pairs...>::is_lazy...);
-  auto operator()(expr<Tag, Childs...> const& ex, Pairs const&... pairs) const DECL_AND_RETURN(op_dispatch<Tag, is_lazy> {
-  }(eval(std::get<0>(ex.childs), pairs...), eval(std::get<1>(ex.childs), pairs...)));
+  decltype(auto) operator()(expr<Tag, Childs...> const &ex,
+                            Pairs const &... pairs) const {
+    return op_dispatch<Tag, is_lazy> {}(eval(std::get<0>(ex.childs), pairs...), eval(std::get<1>(ex.childs), pairs...));
+  }
  };
 
 // the general case for more than 2 nodes. I put 1 and 2 nodes apart, just because it is the most frequent
diff --git a/triqs/gfs/bz.hpp b/triqs/gfs/bz.hpp
index bb397348..7aa97206 100644
--- a/triqs/gfs/bz.hpp
+++ b/triqs/gfs/bz.hpp
@@ -50,10 +50,13 @@ namespace gfs {
 
   // simple evaluation : take the point on the grid...
   template <> struct evaluator_fnt_on_mesh<bz> {
-   lattice::k_t k;
+   size_t n;
    evaluator_fnt_on_mesh() = default;
-   template <typename MeshType> evaluator_fnt_on_mesh(MeshType const &m, lattice::k_t const &k_) { k = k_; }
-   template <typename F> auto operator()(F const &f) const DECL_AND_RETURN(f(k));
+   template <typename MeshType> evaluator_fnt_on_mesh(MeshType const &m, lattice::k_t const &k) { 
+    n = m.locate_neighbours(k); // TO BE IMPROVED
+   }
+   //template <typename F> auto operator()(F const &f) const DECL_AND_RETURN(f(k));
+   template <typename F> decltype(auto) operator()(F const &f) const { return f(n); }
   };
 
   // ------------- evaluator  -------------------
diff --git a/triqs/gfs/curry.hpp b/triqs/gfs/curry.hpp
index c7e38798..8384aae4 100644
--- a/triqs/gfs/curry.hpp
+++ b/triqs/gfs/curry.hpp
@@ -44,7 +44,7 @@ namespace triqs { namespace gfs {
   template<typename ... Ms> struct cart_prod_impl;
   template<typename ... Ms> using cart_prod = typename cart_prod_impl<Ms...>::type;
   template<typename ... Ms> struct cart_prod_impl<std::tuple<Ms...>> { using type = cartesian_product<Ms...>;};
-  template<typename M> struct cart_prod_impl<std::tuple<M>> { typedef M type;}; //using type = M;};
+  template<typename M> struct cart_prod_impl<std::tuple<M>> { using type = M;};
 
   template<typename M0, typename M1, typename ...M> auto rm_tuple_of_size_one(std::tuple<M0,M1,M...> const & t) DECL_AND_RETURN(t);
   template<typename M> auto rm_tuple_of_size_one(std::tuple<M> const & t) DECL_AND_RETURN(std::get<0>(t));
@@ -55,9 +55,9 @@ namespace triqs { namespace gfs {
   template<typename ... T> std::tuple<T...> const &  as_tuple(std::tuple<T...> const & x) { return x;}
   template<typename ... T> std::tuple<T...> & as_tuple(std::tuple<T...> & x) { return x;}
 
-  template<int ... pos, typename Opt, typename Target, bool B, bool IsConst, typename IT, typename ... Ms>
-  gf_view< typename cart_prod_impl< triqs::tuple::filter_out_t<std::tuple<Ms...>, pos...>>::type ,Target, Opt,IsConst>
-   partial_eval(gf_impl< cartesian_product<Ms...>, Target,Opt,B,IsConst> const & g, IT index) { 
+  template <int... pos, typename Opt, typename Target, bool IsConst, typename IT, typename... Ms>
+  gf_view<cart_prod<triqs::tuple::filter_out_t<std::tuple<Ms...>, pos...>>, Target, Opt, IsConst>
+  partial_eval(gf_view<cartesian_product<Ms...>, Target, Opt, IsConst> g, IT index) {
     // meshes of the returned gf_view : just drop the mesh of the evaluated variables
     auto meshes_tuple_partial = triqs::tuple::filter_out<pos...>(g.mesh().components());
     // a view of the array of g, with the dimension sizeof...(Ms)
@@ -65,12 +65,24 @@ namespace triqs { namespace gfs {
     // now rebuild a tuple of the size sizeof...(Ms), containing the indices and range at the position of evaluated variables.
     auto arr_args = triqs::tuple::inverse_filter<sizeof...(Ms),pos...>(as_tuple(index), arrays::range());
     // from it, we make a slice of the array of g, corresponding to the data of the returned gf_view
-    auto arr2 =  triqs::tuple::apply(arr, arr_args);
+    auto arr2 =  triqs::tuple::apply(arr, std::tuple_cat(arr_args, std::make_tuple(arrays::ellipsis{})));
     // finally, we build the view on this data. 
     using r_t = gf_view< cart_prod< triqs::tuple::filter_out_t<std::tuple<Ms...>, pos...>> ,Target, Opt,IsConst>;
     return r_t{ rm_tuple_of_size_one(meshes_tuple_partial), arr2,  typename r_t::singularity_non_view_t{}, typename r_t::symmetry_t{} };
    }
 
+  template <int... pos, typename Opt, typename Target, typename IT, typename... Ms>
+  gf_view<cart_prod<triqs::tuple::filter_out_t<std::tuple<Ms...>, pos...>>, Target, Opt, false>
+  partial_eval(gf<cartesian_product<Ms...>, Target, Opt> & g, IT index) {
+   return partial_eval<pos...>(g(),index);
+  }
+
+  template <int... pos, typename Opt, typename Target, typename IT, typename... Ms>
+  gf_view<cart_prod<triqs::tuple::filter_out_t<std::tuple<Ms...>, pos...>>, Target, Opt, true>
+  partial_eval(gf<cartesian_product<Ms...>, Target, Opt> const& g, IT index) {
+   return partial_eval<pos...>(g(),index);
+  }
+ 
   /// ---------------------------  curry  ---------------------------------
   // curry<0>(g) returns : x-> y... -> g(x,y...)
   // curry<1>(g) returns : y-> x,z... -> g(x,y,z...)
diff --git a/triqs/gfs/product.hpp b/triqs/gfs/product.hpp
index 0f4f11cd..d08d7d46 100644
--- a/triqs/gfs/product.hpp
+++ b/triqs/gfs/product.hpp
@@ -92,7 +92,10 @@ namespace gfs {
   struct data_proxy<cartesian_product<Ms...>, matrix_valued, Opt> : data_proxy_array<std::complex<double>, 3> {};
   template <int R, typename Opt, typename... Ms>
   struct data_proxy<cartesian_product<Ms...>, tensor_valued<R>, Opt> : data_proxy_array<std::complex<double>, R + 1> {};
-
+ 
+  template <typename Opt, typename M0>
+  struct data_proxy<cartesian_product<M0,imtime>, matrix_valued, Opt> : data_proxy_array<double, 3> {};
+  
   /// ---------------------------  evaluator ---------------------------------
 
   /**
diff --git a/triqs/lattice/bz_mesh.cpp b/triqs/lattice/bz_mesh.cpp
index 4996ef07..2ef1aad5 100644
--- a/triqs/lattice/bz_mesh.cpp
+++ b/triqs/lattice/bz_mesh.cpp
@@ -45,7 +45,7 @@ namespace lattice {
    }
    pos++;
   }
-  return pos;
+  return pos_min;
  }
 
  /// Write into HDF5
diff --git a/triqs/utility/tuple_tools.hpp b/triqs/utility/tuple_tools.hpp
index d9deebe7..732c6e53 100644
--- a/triqs/utility/tuple_tools.hpp
+++ b/triqs/utility/tuple_tools.hpp
@@ -35,15 +35,15 @@ namespace std {
   template<typename ... T> _triqs_reversed_tuple<std::tuple<T...>const &> reverse(std::tuple<T...> const & x) { return {x};}
 
   template<int pos, typename TU> auto get(_triqs_reversed_tuple<TU> const & t) 
-   DECL_AND_RETURN(std::get<std::tuple_size<typename std::remove_const<typename std::remove_reference<TU>::type>::type>::value-1-pos>(t._x));
+   DECL_AND_RETURN(std::get<std::tuple_size<std14::decay_t<TU>>::value-1-pos>(t._x));
   
   template<int pos, typename TU> auto get(_triqs_reversed_tuple<TU> & t)       
-   DECL_AND_RETURN(std::get<std::tuple_size<typename std::remove_const<typename std::remove_reference<TU>::type>::type>::value-1-pos>(t._x));
+   DECL_AND_RETURN(std::get<std::tuple_size<std14::decay_t<TU>>::value-1-pos>(t._x));
   
   template<int pos, typename TU> auto get(_triqs_reversed_tuple<TU> && t)      
-   DECL_AND_RETURN(std::get<std::tuple_size<typename std::remove_const<typename std::remove_reference<TU>::type>::type>::value-1-pos>(move(t)._x));
+   DECL_AND_RETURN(std::get<std::tuple_size<std14::decay_t<TU>>::value-1-pos>(move(t)._x));
 
-  template<typename TU> class tuple_size<_triqs_reversed_tuple<TU>>         : public tuple_size<typename std::remove_const<typename std::remove_reference<TU>::type>::type>{};
+  template<typename TU> class tuple_size<_triqs_reversed_tuple<TU>>         : public tuple_size<std14::decay_t<TU>>{};
 }
 
 
@@ -177,7 +177,7 @@ namespace triqs { namespace tuple {
  };
 
  template<typename F, typename T1>
-  auto apply_on_tuple (F && f,T1 && t1) DECL_AND_RETURN( apply_on_tuple_impl<std::tuple_size<typename std::remove_const<typename std::remove_reference<T1>::type>::type>::value-1>()(std::forward<F>(f),std::forward<T1>(t1)));
+  auto apply_on_tuple (F && f,T1 && t1) DECL_AND_RETURN( apply_on_tuple_impl<std::tuple_size<std14::decay_t<T1>>::value-1>()(std::forward<F>(f),std::forward<T1>(t1)));
 
  /**
   * apply_on_zip(f, t1,t2)
@@ -197,7 +197,7 @@ namespace triqs { namespace tuple {
  };
 
  template<typename F, typename T1, typename T2>
-  auto apply_on_zip (F && f,T1 && t1, T2 && t2) DECL_AND_RETURN( apply_on_zip_impl<std::tuple_size<typename std::remove_const<typename std::remove_reference<T1>::type>::type>::value-1>()(std::forward<F>(f),std::forward<T1>(t1),std::forward<T2>(t2)));
+  auto apply_on_zip (F && f,T1 && t1, T2 && t2) DECL_AND_RETURN( apply_on_zip_impl<std::tuple_size<std14::decay_t<T1>>::value-1>()(std::forward<F>(f),std::forward<T1>(t1),std::forward<T2>(t2)));
 
  /**
   * apply_on_zip(f, t1,t2,t3)