In 2010 Chang Hsu, owner of four of the top seven go titles in Japan (where he is known as Cho U), began teaching his four-year-old daughter to play--on a four-by-four board. To make the game interesting, instead of black and white stones he used red and green discs resembling apples, with a board designed to look like an apple tree. His daughter was quite pleased.
In January 2012 the results of his experience with his daughter appeared in the form of a book entitled Yonro no Go no Hon (Four-Line Go Book). The book takes the reader through the basic rules, techniques for capturing stones, territory, double life, and ko, and has a final challenge section. Mainly it is a collection of 100 puzzle-like problems, red to play and win, each with the answer shown in diagrams on the next page. The text is in Japanese, but the diagrams are self-explanatory.
As the author says, the problems are not particularly hard, but they are not trivial either. They take you through snapbacks and eyes and then into ko timing and under-the-stones tricks. You soon realize that they come from a clever and creative mind. In one problem, for example, red wins by sacrificing seven stones--on a four-by-four board (see image at the bottom)! The problems do not teach much about standard life and death shapes or tesuji--the board is too small for that--but they are an excellent way to practise reading a situation out, move by move, until you see it completely and arrive at a definite conclusion. For learning that all-important skill, the four-by-four board may be just the right place to start.
The publisher (Gentosha) also sells a boxed set including the board, the apples, and a booklet with an earlier set of elementary problems. For those interested in go visibility, this is an excellent tool. The board does not take up much space at a cafe or bar, a game does not take more than a few minutes to finish, and the apple tree is a good eye-catcher. It will not be hard to get someone interested, and then you can use the puzzle problems, or you can just play a few games (the interesting challenge is to make sure your novice opponent wins most of them).
Better yet, there are now i-phone/i-pad app versions available in three languages, with the apples replaced by animal characters in a story mode and by normal black and white stones in a serious mode. Easier to obtain than the book or boxed set, these apps are a bargain for players at all levels, including dan levels. Highly recommended.