What's the relation that joins the nodes? Open the image in a new tab if you'd like to see the diagram with better resolution.

[![enter image description here](https://i.stack.imgur.com/xtV41.png)](https://i.stack.imgur.com/xtV41.png)

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* [What's the graph relation? #1](https://puzzling.stackexchange.com/questions/97643/whats-the-graph-relation-1)

Hint 1

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>  It is equally important to think about why any given two nodes are connected as it is to consider why they are not connected.
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