What is the smallest territory in go that can be successfully invaded?
I've seen and played a version of this were you put the black stones along the center lines of a regular 19x19 board so you carve out a 9x9 space. White is then supposed to create a living group inside. For players of equal strength this is approximately a fair game. I'm not sure what the result of perfect play for either side would be but I'm pretty sure this is the edge case. So 8x8 should be killable if both sides know what they are doing and 10x10 should live. The interesting lines of play for a 9x9 space usually start with white playing the 3-3 point and black answering on the 2-2 point.