<https://secure.gravatar.com/avatar/3a074971b2983c7b50fc9da77051411e?s=96&amp;d=mm&amp;r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.ablison.com/pros-and-cons-of-second-step-curriculum/>