I’m extremeley confused by this, can someone explain or point to a proof of this? How do we get from an uncountable original set to a countable set of non-zero results?
Like I get that if sum of f(x) is absolutely convergent, it means it’s going down fast enough, but it doesn’t mean any of those values are literally zero, does it? So why would we expect that filtering an uncountable set by zero would somehow give us a countable set?