I have to admit, I am partial to the rule that you use a/an based on the first sound of the head noun of the noun phrase, rather than the following word
@nohat Notice how improved this sentence is by removing the -ly adverb: “I can only see laughing at the ‘grammarians’ (qu’est-ce que c’est que ça?) who say such.”
Yikes! What is it about scientists and mathematicians that they co-opt ordinary words to mean something very technical, and then assume that all uses of that word necessarily conform to their technical definition?