<https://ru.coursera.org/learn/modern-combinatorics#mooc>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://ru.coursera.org/lecture/modern-combinatorics/posliedovatiel-nosti-viektorov-dokazatiel-stvo-utvierzhdieniia-A4VMo?authMode=signup>