<https://www.amii.ca/latest-from-amii/conditions-avoiding-node-re-expansions-bounded-suboptimal-search/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.amii.ca/latest-from-amii/conditions-avoiding-node-re-expansions-bounded-suboptimal-search/>