Hey that’s a good find! Share here if you find a solution to your particular case.
It’s actually very useful to understand that you really never need to know how to “implement” a function f(x). Rather, you need a way to implement the inequality f(x) \leq y (or, f(x) \geq y if f is concave). Any set of equations that returns the same subset on (x,y) is a valid implementation of f(x) \leq y. That’s what the user is doing in that post.