I implied that Polygons, cant have holes, but most mathematicians define them so that they can have holes. Anyways, I think you defined them the former, way so I was going with that. In the latter case, my example of a non convex polyhedron with Euler characteristic 3 is a pretty useful one.

## oops mistake in my comment

I implied that Polygons, cant have holes, but most mathematicians define them so that they can have holes. Anyways, I think you defined them the former, way so I was going with that. In the latter case, my example of a non convex polyhedron with Euler characteristic 3 is a pretty useful one.