may select the license of your choice. English author name string: Roman Oleinik URL: https://commons.wikimedia.org/wiki/user:Rustedstrings Wikimedia username:
DescriptionOleinik and Tikhonov.jpg English: Olga Arsenievna Oleinik and Andrey Nikolayevich Tychonoff 1976. Deutsch: Olga Arsenjewna Oleinik und Andrei