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.
Tietzecrossings.svg planar drawing of Tietze's graph with crossings the minimum possible own David Eppstein other versions cczero Uploaded with Tietze's graph
Page 2023 Free-images.com. All images are Public Domain