Many decades ago, Japanese professional Go-Moku players stated that Go
-Moku (five-in-a-row on a horizontally placed 15 x 15 board) is a won
game for the player to move first. So far, this claim has never been s
ubstantiated by (a tree of) variations or by a computer program. Meanw
hile, many variants of Go-Moku with slightly different rules have been
developed. This paper shows that for two common variants, the game-th
eoretical value has been established. Moreover, the Go-Moku program Vi
ctoria is described. It uses two new search techniques: threat-space s
earch and proof-number search. One of the results is that Victoria is
bound to win against any (optimal) counterplay if it moves first. Furt
hermore, it achieves good results as a defender against nonoptimally p
laying opponents. In this contribution we focus on threat-space search
and its advantages compared to conventional search algorithms.