This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
ZingerVJODvizheniiSvobodnojZhidkojMassy. The last page of the article Vasily Zinger ru mathnet ru phtml jrnid sm paperid what fullt optionlang rus ru PDold books Books by Vasily Zinger Russian Mathematics books Drawings and tables with transparent background
Page 2023 Free-images.com. All images are Public Domain