Which article in front of O(.), Ω(.), ...? Writing a survey, I am confronted to a very difficult and -- I dare say -- deep issue: I have many sentences mentioning or stating results of the form "a $\Omega(\sqrt{n})$ lower bound", or "a $O(\sqrt{n}/\varepsilon^2)$ algorithm". And I am struggling to decide whether I should use "a" or "an" in front of these: is there a consensus/precedent?

(in hindsight, this may not be the best place to raise such profound questions; I was just unable to find any better one)
Write it as you pronounce it: "an omega". Or, especially when it can be pronounced with a vowel or consonant, rephrase to avoid the issue: "a bound of..."