The positive curvature is convex rather than concave, and it would imply a universe shaped like the surface of a sphere. In a sphere, two parallel lines would not remain parallel forever ...

They discern one another's shape both by touching and by seeing how the lines appear to change in length as the inhabitants move around one another. One day, a sphere appears before the square.

[DaveMakesStuff] demonstrates a great technique for 3D printing a sphere; a troublesome shape for filament-based printers to handle. As a bonus, it uses a minimum of filament. His ideas can be ...