     let isbn: String
     let authorIntroduction: String
     let summary: String
+    var series: Series?
 }
 
 // MARK: CodingKey

        case isbn = "isbn13"
        case authorIntroduction = "author_intro"
        case summary
    }
}
// MARK: Inner Struct Defines

        let title: String
    }
    
    struct Series: Codable {
        let seriesID: String
        let title: String
        enum CodingKeys: String, CodingKey {
            case seriesID = "id"
            case title
        }
    }
}

