Abstract. In the game of Go we develop a consistent procedural definition of the status of life-and-death problems. This computationally efficient procedure determines the number of external ko threats that are necessary and sufficient to win, and in the case of positions of the type of bent-4-in-the-corner it finds that they are unconditionally dead in agreement with common practice. A rigorous definition of the status of life-and-death problems became necessary for building a library of monolithic eyes (eyes surrounded by only one chain). It is also needed for comparisons of life-and-death programs when solving automatically thousands of problems to analyse whether different results obtained by different programs are due to different status definitions or due to bugs.

Introduction

Overview. In this contribution we describe a project whose aim was to built a data base of eyes together with their life-and-death status which at least reflects one aspect of ko accurately: the number of necessary external ko threats for the weaker side to win. The procedure how to determine this number is described in Section 2. After that we seem to be ready for determining the status of a life-and-death problem if there would not be the bent-4-in-the-corner positions (in the following called bent-4) which are characterized in Section 3 and force us in Section 4 to refine the procedure that we take as the (procedural) definition of the status of a life-and-death problem.