Class & operator's |Error: undefined reference to operator

#ifndef FRACTION_H_INCLUDED
#define FRACTION_H_INCLUDED
#include <iostream>
using namespace std;
class Fraction {
private:
    long long x;
    unsigned short y;
public:
    Fraction() : x(0), y(0){};
    Fraction(long long _x, unsigned short _y): x(_x), y(_y){};
    friend ostream& operator<<(ostream& os, const Fraction &X);
    friend Fraction operator+(const Fraction &X, const Fraction &Y);
    friend Fraction operator-(const Fraction &X, const  Fraction &Y);
    friend Fraction operator*(const Fraction &X, const Fraction &Y);
    friend const bool operator>(const Fraction &X, const Fraction &Y);
    friend const bool operator<(const Fraction &X, const Fraction &Y);
    friend const bool operator>=(const Fraction &X, const Fraction &Y);
    friend const bool operator<=(const Fraction &X, const Fraction &Y);
    friend const bool operator==(const Fraction &X, const Fraction &Y);
    friend const bool operator!=(const Fraction &X, const Fraction &Y);
    ~Fraction() {};
};
#endif // FRACTION_H_INCLUDED

#include "fraction.h"
 
ostream& operator <<(ostream &os, const Fraction &X){
    os << X.x << "." << X.y;
    return os;
}
 
const bool operator ==(const Fraction &X, const Fraction &Y){
    if((X.x==Y.x) && (X.y==Y.y)) return true;
    else                     return false;
}
 
const bool operator !=(const Fraction &X, const Fraction &Y){
    return !(X == Y);
}
 
const bool operator <=(const Fraction &X, const Fraction &Y){
    if ((X.x <= Y.x) && (X.y <= Y.y)) return true;
    else                          return false;
}
 
const bool operator >=(const Fraction &X, const Fraction &Y){
    if ((X.x >= Y.x) && (X.y >= Y.y)) return true;
    else                          return false;
}
 
const bool operator <(const Fraction &X, const Fraction &Y){
    if ((X.x < Y.x) && (X.y < Y.y)) return true;
    else                        return false;
}
 
const bool operator >(const Fraction &X, const Fraction &Y){
    if ((X.x > Y.x) && (X.y > Y.y)) return true;
    else                        return false;
}
 
Fraction operator +(const Fraction &X, const Fraction &Y){
    return Fraction(X.x+Y.x, X.y+Y.y);
}
 
Fraction operator -(const Fraction &X, const Fraction &Y){
    return Fraction(X.x - Y.x, X.y - Y.y);
}
 
Fraction operator *(const Fraction &X, const Fraction &Y){
    return Fraction(X.x * Y.x, X.y * Y.y);
}

#include <iostream>
#include "fraction.h"
 
using namespace std;
 
int main(void)
{
    Fraction X(2, 23), Y(2, 22);
    cout << "a: " << X << "   b: " << Y << endl << endl;
    cout << "a + b = " << X+Y << endl;
    cout << "a - b = " << X-Y << endl;
    cout << "a * b = " << X*Y << endl;
 
    if(X < Y) cout << "a < b" << endl;
    else      cout << "a > b" << endl;
 
    if(X == Y) cout << "a == b" << endl;
    else       cout << "a != b" << endl;
    return 0;
}