///Shift a maps with a constant.

   ///This \ref concept::ReadMap "read only map" returns the sum of the

   ///given map and a constant value.

   ///Its \c Key and \c Value is inherited from \c M.

   ///

   ///Actually,

   ///\code

   ///  ShiftMap<X> sh(x,v);

   ///\endcode

   ///it is equivalent with

   ///\code

   ///  ConstMap<X::Key, X::Value> c_tmp(v);

   ///  AddMap<X, ConstMap<X::Key, X::Value> > sh(x,v);

   ///\endcode

   template<class M> 

   class ShiftMap

   {

     const M &m;

     typename M::Value v;

   public:

     typedef typename M::Key Key;

     typedef typename M::Value Value;

     ///Constructor

     ///Constructor

     ///\param _m is the undelying map

     ///\param _v is the shift value

     ShiftMap(const M &_m,const Value &_v ) : m(_m), v(_v) {};

     Value operator[](Key k) const {return m[k]+v;}

   };

   ///Returns an \ref ShiftMap class

   ///This function just returns an \ref ShiftMap class.

   ///\relates ShiftMap

   ///\todo A better name is required.

   template<class M> 

   inline ShiftMap<M> shiftMap(const M &m,const typename M::Value &v) 

   {

     return ShiftMap<M>(m,v);

   }

   ///Scale a maps with a constant.

   ///This \ref concept::ReadMap "read only map" returns the value of the

   ///given map multipied with a constant value.

   ///Its \c Key and \c Value is inherited from \c M.

   ///

   ///Actually,

   ///\code

   ///  ScaleMap<X> sc(x,v);

   ///\endcode

   ///it is equivalent with

   ///\code

   ///  ConstMap<X::Key, X::Value> c_tmp(v);

   ///  MulMap<X, ConstMap<X::Key, X::Value> > sc(x,v);

   ///\endcode

   template<class M> 

   class ScaleMap

   {

     const M &m;

     typename M::Value v;

   public:

     typedef typename M::Key Key;

     typedef typename M::Value Value;

     ///Constructor

     ///Constructor

     ///\param _m is the undelying map

     ///\param _v is the scaling value

     ScaleMap(const M &_m,const Value &_v ) : m(_m), v(_v) {};

     Value operator[](Key k) const {return m[k]*v;}

   };

   ///Returns an \ref ScaleMap class

   ///This function just returns an \ref ScaleMap class.

   ///\relates ScaleMap

   ///\todo A better name is required.

   template<class M> 

   inline ScaleMap<M> scaleMap(const M &m,const typename M::Value &v) 

   {

     return ScaleMap<M>(m,v);

   }