colorisation de surface 3D : surface de Boy :
Surface[2 / 3 (cos(u) cos(2v) + sqrt(2) sin(u) cos(v)) cos(u) / (sqrt(2) - sin(2u) sin(3v)),
2 / 3 (cos(u) sin(2v) - sqrt(2) sin(u) sin(v)) cos(u) / (sqrt(2) - sin(2u) sin(3v)),
sqrt(2) cos(u) cos(u) / (sqrt(2) - sin(2u) sin(3v)),
u, 0, π, v, 0, π]
White... Black... wait...
