default.go
func (u *ISBN13) DeepCopy() *ISBN13 {
	if u == nil {
		return nil
	}
	out := new(ISBN13)
	u.DeepCopyInto(out)
	return out
}
func (u *ISBN13) DeepCopy() *ISBN13 {
	if u == nil {
		return nil
	}
	out := new(ISBN13)
	u.DeepCopyInto(out)
	return out
}
// DeepCopy copies the receiver into a new ISBN13.