Keep Fit!

Some people may think that the 5×5 board is just a reduced version of Go. Fukui Masaaki's little creations show that much of what is complex and profound in Go can be found in the tight confines of the 5×5 board. The problems cover endgame moves, aspects of life and death, attacking and defending, judgments based on calculating territory, the presence or absence of ko threats, and even things pertaining to the realm of middle game fighting.
Not only is this book useful for improving your understanding of shapes and techniques, it is also a lot of fun!