It is an error (see my comment). You can graph
on Desmos.com by looking at the complement of
The Unshaded region below is the graph of your equation.

Alternatively, taking the complement of

Floor function error in Desmos? - Mathematics Stack Exchange
how do you type y=[[x]] in desmos?
Continuous approximations of the Floor and Ceiling functions
A bug with the floor function.
I think I know why, desmos uses a font that combines f and l characters into one connected graphic, so when you go in between them, the f still renders as the fl character, but the l comes off, so it looks as if it appears twice
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It is an error (see my comment). You can graph
on Desmos.com by looking at the complement of
The Unshaded region below is the graph of your equation.

Alternatively, taking the complement of

It is not difficult to show that if and only if
.
Try graphing in Desmos

Desmos does not show it accurately on the boundaries, however.
It is also the case that if and only if
, but Desmos errs once again on the boundary.

i am looking to graph the integer-only line, but whenever i try to type [[]], it tells me that you cannot store a list of numbers in a list.
Inspired by the "absolute value of x without using absolute value" I thought I'd try to do the floor and ceiling function. Not an exact solution but it was fun!