<https://www.classcraft.com/resources/blog/heterogeneous-vs-homogeneous-grouping-whats-the-best-way-to-group-students/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.classcraft.com/blog/heterogeneous-vs-homogeneous-grouping-whats-the-best-way-to-group-students/>