The truncated journal page shown below is an excerpt from Monthly Notices of the Royal Astronomical Society.

The geometry employed (i.e., “straight lines starting from a point come back to their origin after having travelled a path of length πR”) references what is called real projective space. This geometry is unintuitive and its technical description, which has been provided strictly as a comparative reference, is intelligible only to a particular group of mathematical specialists. THE READER IS NOT EXPECTED TO UNDERSTAND THIS MATERIAL.