Fraction (improved)

using System;

namespace Fraction
{
    public static class IntExtensions
    {
        public static int GCD(this int a, int b)
        {
            while (a != b)
                if (a > b) a -= b;
                else b -= a;

            return Math.Max(a, b);
        }
    }

    public class Fraction
    {
        private int _numerator;
        private int _denominator = 1;

        public int Numerator
        {
            get => _numerator;
            set
            {
                _numerator = value;
                Reduce();
            }
        }

        public int Denominator
        {
            get => _denominator;
            set
            {
                if (value == 0)
                    throw new DivideByZeroException();

                _denominator = value;
                Reduce();
            }
        }

        public Fraction(int numerator, int denominator)
        {
            (Numerator, Denominator) = (numerator, denominator);
        }

        public static Fraction operator +(Fraction fraction) => fraction;
        public static Fraction operator -(Fraction fraction)
            => new Fraction(-fraction.Numerator, fraction.Denominator);

        public static Fraction operator +(Fraction a, Fraction b)
            => new Fraction(
                a.Numerator * b.Denominator + b.Numerator * a.Denominator,
                a.Denominator * b.Denominator
            );

        public static Fraction operator -(Fraction a, Fraction b)
            => a + (-b);

        public static Fraction operator *(Fraction a, Fraction b)
            => new Fraction(a.Numerator * b.Numerator, a.Denominator * b.Denominator);

        public static Fraction operator /(Fraction a, Fraction b)
            => new Fraction(a.Numerator * b.Denominator, a.Denominator * b.Numerator);

        public override string ToString() => $"{Numerator} / {Denominator}";

        public void Reduce()
        {
            NormalizeSign();

            var gcd = Math.Abs(_numerator)
                .GCD(Math.Abs(_denominator));

            _numerator /= gcd;
            _denominator /= gcd;
        }

        private void NormalizeSign()
        {
            var sign = Math.Sign(_numerator * _denominator);
            _denominator = Math.Abs(_denominator);
            _numerator *= sign;
        }
    }

    class Program
    {
        static void Main()
        {
            var a = new Fraction(1, 2);
            var b = new Fraction(1, 4);

            Console.WriteLine(a + b);
            Console.WriteLine(a / b);
        }
    }
}