esempio di superficie non orientabile e di superficie rigata
mathlinks: http://mathworld.wolfram.com/MoebiusStrip.html
Like the cylinder, it is not a true surface, but rather a surface with boundary
The Möbius strip has Euler characteristic $ ~\chi=0 $
A Möbius strip of half-width w with midcircle of radius R and at height z=0 can be represented parametrically by
$ $x = [R+s\cos{(\frac 1 2 t)}]\cos{t} $
$ $y = [R+s\cos{(\frac1 2 t)}]\sin{t} $
$ $z = s\sin{(\frac 1 2 t)} $
for s in [-w,w] and t in $ ~[0,2\pi) $. In this parametrization, the Möbius strip is therefore a cubic surface with equation
$ $-R^2y+x^2y+y^3-2Rxz-2x^2z-2y^2z+yz^2=0. $
forme musicali
Canone 1 a 2 dell’”Offerta musicale” di J. S. Bach (1747)
http://strangepaths.com/canone-1-a-2/2009/01/18/it/
continua...
