Thread: Unable to see enclosed private class?

I have a class (Quadtree) and three inner class inside (Node, Inner and Leaf). Inner and Leaf inherit from Node.
I have a function in the private scope of Quadtree.
All these are located in fun.h .
Then, in fun.cpp, I am implementing the function (which is named foo <- what a prototype name!), which takes as argument a pointer to an Inner object. Inner seems unable to be resolved however!

fun.h

Code:

class Quadtree {
private:

class Node{
public:
        Node() { std::cout << "Node\n"; }
};

class Inner : public Node {
public:
        Inner() { std::cout << "Inner\n"; }
        friend class Quadtree;
};

class Leaf : public Node {
public:
        Leaf() { std::cout << "Leaf\n"; }
        friend class Quadtree;
};


int foo(Inner* p);
public:
        Quadtree() { std::cout << "Quadtree\n"; }

};

fun.cpp

Code:

#include <iostream>
#include "fun.h"

int foo(Inner* p) { std::cout << "foo\n"; }

px.cpp

Code:

#include <iostream>
#include "fun.h"

int main()
{
        Quadtree tree;
        return 0;
}

Compilation & error:

Code:

samaras@samaras-A15:~$ g++ px.cpp fun.cpp -o px
fun.cpp:4:9: error: ‘Inner’ was not declared in this scope
fun.cpp:4:16: error: ‘p’ was not declared in this scope
fun.cpp:4:19: error: expected ‘,’ or ‘;’ before ‘{’ token

In fun.cpp it should be Quadtree::foo.

I am ridiculous, sorry...