A diptych (/ˈdɪptɪk/; from the Greek δίπτυχον,[1] di "two" + ptychē "fold") is any object with two flat plates which form a pair, often attached by hinge. For example, the standard notebook and school exercise book of the ancient world was a diptych consisting of a pair of such plates that contained a recessed space filled with wax. Writing was accomplished by scratching the wax surface with a stylus.