- Boulevard Park, Washington (Wikipedia)
Boulevard Park is a census-designated place (CDP) in King County, Washington, United States. The population was 5,287 at the 2010 census. Boulevard Park was part of the Riverton-Boulevard Park CDP in 2000 but was split for the 2010 census into its own CDP.
- 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.