This is a kind of silly question, but I don't know where else to ask. Suppose I wanted to say "Ceci n'est pas une pipe" but with $K(\pi,n)$ substituted for "pipe." Would the article be "un" or "une"?
In case there are additional complications in the translation: What would be the French for "This is not a $K(\pi,n)$," where "this" refers to a picture over/under/beside the text?