How to Improve on a 5x5 Board
How to Improve on a 5x5 board - 囲碁特訓 五×五―五道盤上達法 Go Super Books Volume 2 By Fukui Masaaki
This is a book of go problems on a 5x5 board. Nicely bound softcover with sleeve. Not hard to figure out even if you don't read Japanese. Reads from right to left, problems on left page, answers on reverse page so you have to turn the page to see them. In Japanese.
Short writeup by John Fairbairn: How to Improve on a 5x5 board (archived)