[In front of a blackboard, in an office at Real College]
Skeptic: And why should I care about holomorphic functions?
Holomorphic enthusiast:$\;$ Can you compute $\quad$ $\sum_{n={-\infty}}^{\infty} \frac{1}{(a+n)^2}$ ? Here $a$ is one of your cherished real numbers, but not an integer.
Skeptic: Well, hm...
Holomorphic enthusiast, nonchalantly: Oh, you just get
$$\sum_{n={-\infty}}^{\infty} \frac{1}{(a+n)^2}=\pi^2 cosec^2 \pi a $$
It's easy using residues.
Skeptic: Well, maybe I should have a look at these "residues".
Holomorphic enthusiast (generously): Let me lend you this introduction to Complex Analysis by Remmert, this one by Lang and this oldie by Titchmarsh. As Hadamard said: "Le plus court chemin entre deux vérités dans le domaine réel passe par le domaine complexe".You can look for a translation at Mathoverflow. They have a nice list of mathematical quotations, following a question there.
Skeptic: Mathoverflow ??
Holomorphic enthusiast (looking a bit depressed) : I think we should have a nice long walk together now.
[Exeunt]
Best Answer
I suggest only numbering expressions which will be referred to later in the paper. If "for future discussion" means a later paper, I think referencing equations in earlier papers solely via a number is a pretty good way to seriously discourage readership.