Watcher

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Base case: we have two correctly recognized positions differing by a single move (single added stone). Easy.

Issues:

  * illegal positions -> ignorable

  * positions unreachable from the previous state

    * reachable from any past state. (Incorrect states inbetween). How to pick the correct leaf of such a tree?

    * reachable by more than one move. Issues with branching factor.

  * board shifts -> repaired manually (or automatically), further positions have to be reevaluated

  * stone shifts

    * stone stops being recognized -> fixable manually and even ignorable