diff --git a/test/triqs/gfs/CMakeLists.txt b/test/triqs/gfs/CMakeLists.txt
index 2b4bb98a..4423d27c 100644
--- a/test/triqs/gfs/CMakeLists.txt
+++ b/test/triqs/gfs/CMakeLists.txt
@@ -1,3 +1,3 @@
 link_libraries (triqs)
 all_tests()
-
+add_subdirectory(multivar)
diff --git a/test/triqs/gfs/g_k_om.cpp b/test/triqs/gfs/g_k_om.cpp
index de207437..7554f8d7 100644
--- a/test/triqs/gfs/g_k_om.cpp
+++ b/test/triqs/gfs/g_k_om.cpp
@@ -23,12 +23,16 @@ int main() {
   // try to assign to expression 
   placeholder<0> k_;
   placeholder<1> w_;
-  auto eps = make_expr( [](k_t const& k) { return -2 * (cos(k(0)) + cos(k(1))); }) ;
 
-  G(k_, w_) << 1 / (w_ - eps(k_) - 1 / (w_ + 2));
+  auto eps_k = -2 * (cos(k_(0)) + cos(k_(1)));
+  G(k_, w_) << 1 / (w_ - eps_k - 1 / (w_ + 2));
 
-  // hdf5 
-  h5::file file("ess_g_k_om.h5", H5F_ACC_TRUNC );
+  // same
+  // auto eps = make_expr( [](k_t const& k) { return -2 * (cos(k(0)) + cos(k(1))); }) ;
+  // G(k_, w_) << 1 / (w_ - eps(k_) - 1 / (w_ + 2));
+
+  // hdf5
+  h5::file file("ess_g_k_om.h5", H5F_ACC_TRUNC);
   h5_write(file, "g", G);
 
  
diff --git a/triqs/clef/clef.c11.hpp b/triqs/clef/clef.c11.hpp
index b76fdf99..cb68c854 100644
--- a/triqs/clef/clef.c11.hpp
+++ b/triqs/clef/clef.c11.hpp
@@ -59,12 +59,19 @@ namespace triqs { namespace clef {
   *  Placeholder and corresponding traits
   *  --------------------------------------------------------------------------------------------------- */
  template<int i, typename T> struct pair; // forward
+ template<typename Tag, typename... T> struct expr; //forward
 
  // a placeholder is an empty struct, labelled by an int.
  template<int N> struct placeholder {
   static_assert( (N>=0) && (N<64) , "Placeholder number limited to [0,63]");
   static constexpr int index = N;
   template <typename RHS> pair<N,RHS> operator = (RHS && rhs) { return {std::forward<RHS>(rhs)};} 
+  template <typename... T> expr<tags::function, placeholder, expr_storage_t<T>...> operator()(T&&... x) const {
+   return {tags::function{}, *this, std::forward<T>(x)...};
+  }
+  template <typename T> expr<tags::subscript, placeholder, expr_storage_t<T>> operator[](T&& x) const {
+   return {tags::subscript{}, *this, std::forward<T>(x)};
+  }
  };
 
  // placeholder will always be copied (they are empty anyway).
diff --git a/triqs/clef/clef.c14.hpp b/triqs/clef/clef.c14.hpp
index 21e51589..2bf90a30 100644
--- a/triqs/clef/clef.c14.hpp
+++ b/triqs/clef/clef.c14.hpp
@@ -58,12 +58,19 @@ namespace triqs { namespace clef {
   *  Placeholder and corresponding traits
   *  --------------------------------------------------------------------------------------------------- */
  template<int i, typename T> struct pair; // forward
+ template<typename Tag, typename... T> struct expr; //forward
 
  // a placeholder is an empty struct, labelled by an int.
  template<int N> struct placeholder {
   static_assert( (N>=0) && (N<64) , "Placeholder number limited to [0,63]");
   static constexpr int index = N;
-  template <typename RHS> pair<N,RHS> operator = (RHS && rhs) { return {std::forward<RHS>(rhs)};} 
+  template <typename RHS> pair<N,RHS> operator = (RHS && rhs) { return {std::forward<RHS>(rhs)};}
+  template <typename... T> expr<tags::function, placeholder, expr_storage_t<T>...> operator()(T&&... x) const {
+   return {tags::function{}, *this, std::forward<T>(x)...};
+  }
+  template <typename T> expr<tags::subscript, placeholder, expr_storage_t<T>> operator[](T&& x) const {
+   return {tags::subscript{}, *this, std::forward<T>(x)};
+  }
  };
 
  // placeholder will always be copied (they are empty anyway).
diff --git a/triqs/lattice/bz_mesh.hpp b/triqs/lattice/bz_mesh.hpp
index 60ca61f3..585262ac 100644
--- a/triqs/lattice/bz_mesh.hpp
+++ b/triqs/lattice/bz_mesh.hpp
@@ -68,6 +68,8 @@ namespace lattice {
    long index() const { return _index; }
    bool at_end() const { return (_index == m->size()); }
    void reset() { _index = 0; }
+   double operator()(int i) const { return m->index_to_point(_index)(i);}
+   double operator[](int i) const { return m->index_to_point(_index)(i);}
   };
 
   /// Accessing a point of the mesh