#ifndef YINGYANGH
#define YINGYANGH

#include <vector>
using namespace std;

class yang;   //forward declaration

class ying {
	yang *p;
	yang& r;
	vector<yang *> v;
public:
	ying(yang& initial_y): p(&initial_y), r(initial_y) {}

	//yang f(yang y) const {return y;}   //won't compile
	yang  f(yang  y) const;
	yang *g(yang *y) const {return y;}
};

class yang {
	ying *p;
	ying& r;
	vector<ying *> v;
public:
	yang(ying& initial_y): p(&initial_y), r(initial_y) {}

	ying  f(ying  y) const {return y;}
	ying *g(ying *y) const {return y;}
};

inline yang ying::f(yang y) const   //Must be written after lines 21-30.
{
	return y;
}
#endif