The "I Used to Know That" 5 Book Collection in a slipcase is a box set of non-fiction learning aids published by Michael O' Mara Books. Written by various authors, this educational collection covers a range of topics presented in an accessible and informative manner. With its compact format and convenient slipcase, this book set is perfect for readers looking to expand their knowledge in a variety of subjects in a quick and easy-to-digest format.bools are fine slipcase shown small sign of wear