[itishappy]

Nice example! A sphere is pretty tough to see...

One thing that helped me is considering how to deform the edges of your glued circle examples into a flat square. First, map the two sides of the seam two the two corners of the plane. This becomes a sphere by folding it into a triangle and then gluing (or portaling) up neighboring edges. Having the portals on neighboring edges means that they change directions in weird ways.

This is somewhat different than the torus with portals example, where the portals were placed on opposite edges of the plane.

Edit: Found some diagrams!

https://en.wikipedia.org/wiki/Fundamental_polygon#Examples_o...