- Klein bottle (Wikipedia)
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.
- Zhuang Zhou (Wikipedia)
Zhuang Zhou (/dʒuˈɑːŋ ˈdʒoʊ/), commonly known as Zhuangzi (/ˈdʒwɑːŋˈdzʌ/; Chinese: 莊子; literally “Master Zhuang”; also rendered in the Wade–Giles romanization as Chuang Tzu), was an influential Chinese philosopher who lived around the 4th century BCE during the Warring States period, a period of great development in Chinese philosophy, the Hundred Schools of Thought. He is credited with writing—in part or in whole—a work known by his name, the Zhuangzi, which is one of two foundational texts of Taoism, alongside the Tao Te Ching.