<https://akademia-matematyki.edu.pl/matura-maj-2011-zadanie-25-uzasadnij-ze-jezeli-ab1-i-a2b27-to-a4b431/#webpage>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://akademia-matematyki.edu.pl/matura-maj-2011-zadanie-25-uzasadnij-ze-jezeli-ab1-i-a2b27-to-a4b431/>