Comparing #360 (version 3) and #361 (version 4)

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In this tree, `I` is considered problematic. Although `C11` has been neutralized by `C21` and `C22`, `C12` still needs to be addressed. In addition, `C23` *would* have neutralized `C13`, but `C31` and `C32` make `C23` problematic again,problematic, so `C13` makes `I` problematic as well.
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