<https://secure.gravatar.com/avatar/8e6543e009db06ab875f55b9f50df521?s=96&amp;d=mm&amp;r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://paperperk.com/blog/how-many-sources-for-a-research-paper>