<https://secure.gravatar.com/avatar/d5ab6c59b72bd3277649f6fe728b5d74?s=96&d=mm&r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.code4example.com/python/python-program-to-calculate-area-and-perimeter-of-triangle/>