Let me try to explain why I voted to close, and why I chose not to answer.
The question, as it is phrased now, seems to ask about very specific aspects of the AKLT model. However, in order to be able provide a specific answer (which does not form a full explanation of the AKLT model), the OP would have to supply sufficient information on their prior knowledge, i.e., lay out the overall scenario considered and their understanding of it to an extent which allows to answer the question in a concise way. The way the question is phrased now, this is not the case: E.g. the screenshot from the paper is far from helpful for an answer and does not really explain which part of the construction the OP understands (also to me, such screenshots to some extent seem like a low-effort sign), one would have to basically explain the whole AKLT model, which would be a disproportional effort compared to the effort which went into the question.
Now I'm not generally against writing a detailed explanation of the AKLT model, but I feel it is slightly lost effort if it is posted as an answer to a question which is seemingly concerned with details -- another poster with questions about the AKLT model will likely not see that the answer contains the full explanation of the model, rather than just assume it is an answer to a very specific question. Now given the apparent current interest in the AKLT model, I might consider writing such an answer for a question asking about the AKLT model in general. (The downside seems to me that as such, such a question -- which would basically just state "Could someone please explain the AKLT model?" might (rightfully) be badly received here.)