We start in line 6 by using list comprehension to eunmerate all ordered pairs \((i, j)\) with \(i\) non-negative, and \(j\) positive, and both \(i, j\) bounded above by some \(N\).
Line 7 defines a function which takes a point and returns the GCD of its two components.
In line 8, we make use of Desmos's logical indexing. \(P_0[g(P_0) = 1]\) is a sub-list of \(P_0\) consisting of all elements \(p \in P_0\) such that \(g(p) = 1\). In other words, we extract from \(P_0\) all elements whose components have GCD equal to 1.
In a similar fashion, line 9 simply extracts from \(Q_0\) the elements whose \(x\) coordinate (numerator) is at most its \(y\) coordinate (denominator). This serves to restrict our rationals to \([0, 1]\).
Finally, in line 10, we render a graph of our function by enumerating all points of the form \(\left( \frac{r}{s}, \frac{1}{s}\right)\) for rationals \(\frac{r}{s}\) with \(\text{GCD}(r, s) = 1\).
The remaining lines serve only aesthetic purposes.