Develops the mathematical techniques for solving late-stage endgame problems in the game Go. As a typical game of Go approaches its conclusion, the active areas of play become independent of one another and the overall board position may be regarded as a sum of disconnected partial board positions. The authors apply combinatorial game theory to solving Go-related problems with a bewildering choice of similar-looking moves and subtle priority relationships. The theory in this book assigns each active area on the board an abstract value and then shows how to compare them to select the optimum move or add them up to determine the ideal outcome. Some of the values are familiar numbers or fractions, but most are bizarre objects not seen before in Go literature. From these abstractions, the reader learns that positions seeming to have the same numerical value can be crucially different, while positions that appear completely different can be mathematically identical.