/// <summary>
/// Returns a hash code for this instances.
/// </summary>
/// <returns>
/// A hash code for this instances, suitable for use in hashing algorithms and data structures like a hash table.
/// </returns>
public override int GetHashCode()
{
return
(this.HasValue.GetHashCode()
^ (Book == null ? 0 : Book.ToLower().GetHashCode())
^ (N1 == null ? 0 : N1.ToLower().GetHashCode() >> 1)
^ (N2 == null ? 0 : N2.ToLower().GetHashCode() << 1)
^ (NumberCount));
}