What is this 90% of? 90% in a life and death problem test? Or looking at a board and correctly saying alive, dead or unsettled(*) for 90% of the chains on the board?Isn't it better to be a trillion trillion times faster and be only 90% sure you solved the problem?you want to solve. Ladder problems need to be solved 99.9999% correctly. For complex life-and-death 90% is more acceptable.