- In mathematics, the Klein bottle (/ˈklaɪn/) is an example of a non-orientable surface; that is, informally, a one-sided surface which, if traveled upon, could be followed back to the point of origin while flipping the traveler upside down. More formally, the Klein bottle is a two-dimensional manifold on which one cannot define a normal vector at each point that varies continuously over the whole manifold. Other related non-orientable surfaces include the Möbius strip and the real projective plane. While a Möbius strip is a surface with a boundary, a Klein bottle has no boundary. For comparison, a sphere is an orientable surface with no boundary.
- World Report 2024: Ukraine (hrw.org)
The human rights impacts of Russia’s war on Ukraine continued to eclipse all other rights issues in Ukraine. As of September, at least 9,614 civilians had been killed and more than 17,535 injured since Russia’s full-scale invasion began in February 2022. Millions more had to flee abroad or were internally displaced.