Plotting mechanics question

Hello!
I’m currently reading docs on chia plotting mechanics (https://www.chia.net/assets/Chia_Proof_of_Space_Construction_v1.1.pdf) and I wonder if someone can help me to understand certain things about it.
Paragraph “Compressing Entry Data”
A line is a set of tuples (x,y). Then why do we say that x(x-1)/2 + y resides on line (second from the bottom formula)

Since

x(x-1)/2 + y

results in a single value, not a tuple, how it can reside on a line? Or I get something wrong?
(sorry, can’t provide more screens due to newbie limitations)

1 Like

In case if someone ever read this post.

Well, I’ve dug up a little and figured out that we can assume this Line just as a set with values, which are hashes of real (x,y) points respectively. But not a real hash, actually, since there’s a bijection between Line and points, i.e. you can always restore point from Line entry and vice versa. Then there’s a delta format and some other hairy math and so on. Anyway, my goal was to find a way to compress a plot as much as possible, and I’ve managed to reach only 5-8%.