A cylinder
If we take a long and narrow rectangle and paste together the two shortest sides after having impressed two half a torsions, we get an anomalous cylinder: the boundary is made of two crossed circumpherences, as in a Hopf link. This is not the case of a common cylinder.
© matematita
immagine di Gian Marco Todesco
The image belongs to the sections...:
From "fragments of topology" (From "XlaTangente")
Further information:
http://www.toonz.com/personal/todesco
