All new classes that are to be included in FARFALLA trees should inherit from the base class F_Node. In C++ , it is not necessary for the new header file to include all the information that is in F_Node.h; instead, the new header file simply indicates to the compiler that the new class inherits from the existing class F_Node. In the example, this is done by the line
class erpNode : public F_Node {
The word public is a C++ technicality which you will understand after reading a C++ text.