Friday, November 1, 2024

A Sphere Has Two Faces

 A sphere has two faces,

where the transition from one face to the next is at the limit of \(180^o\), internal angle.  One face in front, the back face completely obscured.  But at \(180^o\) internal angle, this sphere has no edge and no vertex.

And so Euler's formular \(F+V=E+2\) is satisfied.