This is the standard model.

Ciro Santilli's preferred visualization of the real projective plane is a small variant of the standard "lines through origin in ${\mathbb{R}}^3$".

Take a open half sphere e.g. a sphere but only the points with $z>0$.

Each point in the half sphere identifies a unique line through the origin.

Then, the only lines missing are the lines in the x-y plane itself.

For those sphere points in the circle on the x-y plane, you should think of them as magic poins that are identified with the corresponding antipodal point, also on the x-y, but on the other side of the origin. So basically you you can teleport from one of those to the other side, and you are still in the same point.

Ciro likes this model because then all the magic is confined just to the $z=0$ part of the model, and everything else looks exactly like the sphere.

It is useful to contrast this with the sphere itself. In the sphere, all points in the circle $z=0$ are the same point. But this is not the case for the projective plane. You cannot instantly go to any other point on the $z=0$ by just moving a little bit, you have to walk around that circle.

The first proper galaxy near the Milky Way is the Andromeda Galaxy. Everything else in the middle is a satellite of either of of those.

Some notable examples:

Chat programs that don't have a proper web-only operation and force you to have a mobile phone, e.g. WhatsApp.

Heck, even Signal, which is supposed to be super secure and good for your privacy, forces you to disclose your freaking cell phone to all contacts! lifehacker.com/how-to-use-signal-without-revealing-your-private-phone-1818996580

What is my phone breaks? What if I don't want to have a fucking phone? What if I move countries and have to change the fucking number? Also evil but less because done by all: chat programs that can't send you an email if you don't see the message in X minutes.

European Union, time to force those evil companies to use support open standards like XMPP?

The solution to "how to prevent spam" is simple: your ID is a public key that you own the private key for. If you start getting spammed, generate a new public key, and send it to all contacts, and dump the previous ID.

It seems impossible to avoid the signaling server. With signaling server:

Games: