template functions intricacies

hello. I hope someone of you c++ gurus can help me out of this.

I am trying to compile something like this:

*********************************************************
template <class M>
class foo {
public:
  class val { public: M p; };
  val v;
  template <class N> void h(foo<N>& c);
};

template <class T, class U>
void g(typename foo<T>::val& a, typename foo<U>::val& b)
{ std::cout << a.p<<","<<b.p<<"\n"; }

template <class M>
template <class N> void foo<M>::h(foo<N>& c)
{ g((*this).v,c.v); /*1*/}

int main(int argc, char*argv[])
{
  foo<int> i1,i2;
  foo<float> f1;
  i1.v.p=1;i2.v.p=2; f1.v.p=0.1;f2.v.p=0.2;
  i1.h(f1);
  i1.h(i2);
  f1.h(i2);
}
***********************************************************

g++ 4.1.2 complains with the error messages

################################
tctc.cpp: In member function 'void foo<M>::h(foo<N>&) [with N = float,
M = int]':
tctc.cpp:37: instantiated from here
tctc.cpp:29: error: no matching function for call to
'g(foo<int>::val&, foo<float>::val&)'
tctc.cpp: In member function 'void foo<M>::h(foo<N>&) [with N = int, M
= int]':
tctc.cpp:38: instantiated from here
tctc.cpp:29: error: no matching function for call to
'g(foo<int>::val&, foo<int>::val&)'
tctc.cpp: In member function 'void foo<M>::h(foo<N>&) [with N = int, M
= float]':
tctc.cpp:39: instantiated from here
tctc.cpp:29: error: no matching function for call to
'g(foo<float>::val&, foo<int>::val&)'
#################################

if I change line /*1*/ making the template function call explicit
  g<M,N>((*this).v,c.v);
everything works fine. so
1) I can't understand this behaviour
2) the problem is not solved by explicitly making the template call
explicit:
    2a) if I declare g (prepending
**
template <class M> class foo;
template <class T,class U> void g(typename foo<T>::val& a, typename
foo<U>::val& b);
**
           to the code above), the problem with the "implicit" call is
not solved, and even the explicit
           "solution" breaks, giving a _linker_ error
##
/tmp/ccsWnHwv.o: In function `void foo<int>::h<float>(foo<float>&)':
tctc.cpp:(.text._ZN3fooIiE1hIfEEvRS_IT_E[void
foo<int>::h<float>(foo<float>&)]+0x14): undefined reference to `void
g<int, float>(foo<int>::val&, foo<float>::val&)'
##
     2b) the explicit call would be a mess if I wanted to play with
overloading, i.e. defining also
*
 template <class T>
void g(typename foo<T>::val& a, typename foo<T>::val& b)
{ std::cout << a.p<<","<<b.p<<"\n"; }
*
          and assuming the compiler to choose properly when to use one
call [e.g. i1.h(f1) ]
          or the other [i1.h(i2)]

thank you!

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