Inheritance in C++, "...is an ambiguous base of ..." error

As written in "The C++ Programming Language 3.Edition - Bjarne Stroustrup". We can use scope solution to prevent ambiguity errors. The basic program which is in below, when i use 3 layer scope in class mix an error occurs. But when i use 2 layer no problem. What is wrong? or is it something like design issue? The error is; ``` deneme.cpp: In constructor ‘mix::mix(std::__cxx11::string, int)’: deneme.cpp:45:22: error: ‘plane’ is an ambiguous base of ‘mix’ pervaneli::plane::engine=b; ``` I don't want to make a diamond model. I am happy with two base (plane) classes. The thing that i just want to learn why it gives error when i use 3 layer scope. Thanks. Note: Version is g++ (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609 ``` #include<iostream> #include<string> using namespace std; class plane{ protected: int speed; string name; public: int engine; void its_name(){ cout<<name<<endl; } plane(int a=10000){ engine=a; } }; class pervaneli:public plane{ public: pervaneli(string a="-"){ name=a; } void belirle(int x){ speed=x; } }; class jet:public plane{ public: jet(string a="-"){ name=a; } void belirle(int x){ speed=x; } }; class mix: public pervaneli,public jet{ public: mix(string a,int b){ jet::name=a; pervaneli::name=a; pervaneli::plane::engine=b; //ambigous base error //pervaneli::engine=b; /*works fine*/ } void belirle(int x){ jet::speed=x; } }; int main() { mix a400m("Alp",9999); a400m.belirle(500); a400m.pervaneli::its_name(); return 0; } ```