109     template<typename Tag, int D = 0> struct case_  : proto::not_<_> {};  struct
111     template<int D> struct case_< proto::tag::plus_assign, D >         : _ {};  struct
112     template<int D> struct case_< proto::tag::minus_assign, D >        : _ {};  struct
113     template<int D> struct case_< proto::tag::multiplies_assign, D >   : _ {};  struct
114     template<int D> struct case_< proto::tag::divides_assign, D >      : _ {};  struct
115     template<int D> struct case_< proto::tag::modulus_assign, D >      : _ {};  struct
116     template<int D> struct case_< proto::tag::shift_left_assign, D >   : _ {};  struct
117     template<int D> struct case_< proto::tag::shift_right_assign, D >  : _ {};  struct
118     template<int D> struct case_< proto::tag::bitwise_and_assign, D >  : _ {};  struct
119     template<int D> struct case_< proto::tag::bitwise_or_assign, D >   : _ {};  struct
120     template<int D> struct case_< proto::tag::bitwise_xor_assign, D >  : _ {};  struct