class Function2D {
	virtual double GetX(double y) {};		// Get the first value
	virtual double GetY(double x) {};
	virtual Array <double> GetX(double y) {};	// Get all values
	virtual Array <double> GetY(double x) {};
};

class Line : public Function2D {
private:
	Point p1, p2;

public:
	Line(Point p1, Point p2) : p1(p1), p2(p2) {};
	
	virtual double GetX(double y);
	virtual double GetY(double x);
};

class Polynomial : public Function2D {
public:
	Polynomial(Point p1, ...);	// Polynomial defined by points
	Polynomial(double coeff, ...);	// Polynomial defined by coefficients
};

... other functions ...