I'm not even sure what title to give this question; hopefully the code will demonstrate what I'm trying to do:

#include <string>
#include <list>
using namespace std;

template<typename A> class Alpha { public: A m_alpha_a; };
template<typename B> class Bravo { public: B m_bravo_b; };

template<> class Alpha<string> { public: string m_alpha_string; };

template<typename B>
template<> class Alpha<Bravo<B> > 
{ 
public: 
    Bravo<B> m_bravo_class;   // Line A
}; 

int main()
{
    Alpha<int> alpha_int;
    alpha_int.m_alpha_a= 4;

    Alpha<string> alpha_string;
    alpha_string.m_alpha_string = "hi";

    Alpha<Bravo<int> > alpha_bravo_int;
    alpha_bravo_int.m_bravo_class.m_bravo_b = 9;
};

I want to write a specialization for Alpha<A> when A is of any type Bravo<B>, but the compiler says

invalid explicit specialization before ‘>’ token
enclosing class templates are not explicitly specialized

(Referring to // Line A.) What's the correct syntax to do what I want?