<https://secure.gravatar.com/avatar/4a19d638521f2ae0e44a62c8226459f3?s=96&amp;d=mm&amp;r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://gdzwow.com/answers/6-matem-uch-dorofeev-peterson-1-nomer-243.html>