Tolong jelaskan mengenai Bacaan tambahan dari Sampul kertas

Hancer, Kevin. (1990) Hancer's Price Guide to Paperback Books, Third Edition, Radnor, Pennsylvania: Wallace-Homestead Book Company. ISBN 0-87069-536-3

Canja, Jeff. (2002) Collectible Paperback Books, Second Edition, East Lansing, MI: Glenmoor Publishing. ISBN 0-9673639