Why is there no such thing as 2 sided polygons?

Answer 1

actually, there is, depending on your definition of polygon, and your definition of a line segment. A line segment is the shortest path btwn two points, right? So take a sphere and pick any two points on that sphere. The shortest path between them on the surface of the sphere would be a "curve" along the surface, but it's the shortest path between the points, so it technally is a line segment. Take two of these line segments that intersect at two points, and there is your two sided polygon!