<https://www.alloteacher.com/2022/03/principles-of-physics-by-jun-ni-in-pdf.html#Breadcrumb>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.alloteacher.com/2022/03/principles-of-physics-by-jun-ni-in-pdf.html>