Pocket self-teaching aid - uses questions and answers on cards held together but placeable on two facing stacks

摘要

Self-teaching aid uses cards with questions on one side and answers on the other. The cards are held together in such a way that from a single stack they can be turned over and placed on either of two different stacks (B, C). The cards are pref. held together by an arm or cord passing through a hole in the edge of each card.