Problems which deal with a liberty filling battle between groups lacking two eyes.
How many points is a move worth? These problems test your counting ability.
When one player well do killing enemy's group, then it's happy. But some cases are impossible to kill. But go is not representing only "winning games". Anyti...
Problems where there's an obvious 2 - 2 cutting point to start the problem.
Problems that let the user choose between several paths of resistance of varying difficulty.
Problems that require the solver to construct a position with some given properties.