offtoppic, c++ and templates

thats an abstract version of the codefragment, and the problem is the error the compiler produces, if you know how to solve it, reply please:

class A{

template <class T> class X : public A{
struct Y : public A{
inline void Add(T *t);

template <class T>
void X<T>::Y::Add(T *t){


=> error LNK2001: Nichtaufgeloestes externes Symbol "public: void __thiscall X<class TMP>::Y::Add(class TMP *)