/* ruban de Moebius */
f(u,r):=[cos(u)*(1+.2*r*cos(u/2)),sin(u)*(1+.2*r*cos(u/2)),.2*r*sin(u/2)];

load(draw);
draw3d(
file_name="moebius",
/* terminal=png, */
surface_hide = true,
xu_grid      = 50,
yv_grid      = 10,
zrange=[-.4,.4],
rot_horizontal=24,
rot_vertical=50,
axis_3d=false,
xtics=false,
ytics=false,
ztics=false,
palette=[3,4,6],
colorbox=false,
parametric_surface(f(u,r)[1],f(u,r)[2],f(u,r)[3],u,-%pi,%pi,r,-1,1) ) ;