<https://www.inspiricapros.com/blog/standardized-tests/gre/whats-covered-in-the-gre-math-section/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.inspiricapros.com/blog/standardized-tests/gre/whats-covered-in-the-gre-math-section/>