 Real projective plane

The real projective plane, often denoted as \(\mathbb{RP}^2\), is a two-dimensional manifold that captures the idea of lines through the origin in three-dimensional space. Here are some key concepts to understand what the real projective plane is: 1. **Definition**: The real projective plane can be defined as the set of all lines through the origin in \(\mathbb{R}^3\).

For some reason, Ciro Santilli is mildly obsessed with understanding and visualizing the real projective plane.

To see why this is called a plane, move he center of the sphere to $z=1$, and project each line passing on the center of the sphere on the x-y plane. This works for all points of the sphere, except those at the equator $z=1$. Those are the points at infinity. Note that there is one such point at infinity for each direction in the x-y plane.