Hint is indeed not a kata suggestion, and don't give hints, all is in the description, the rest is up to the user, thinking, doing researches and not reading discussion page.

When I showed this code to my colleage he said it is Lisp. I did some digging on that website and found fragment suggesting this is Scheme variant of Lisp. I even found online compiler for this, but was unable to run any copy-pasted code there without errors.

But I don't think you need to be familiar with that language to understand their examples. The most important information my colleague gave me is that in Lisp operator precedes arguments, so for example * a b would be a * b in C.

This was a bit more difficult than I expected on 4 kyu...
I liked it, but I didn't plan to spend half of my day with debugging today. :)

Agree. There's nothing difficult about the solution, but due to the problem's complexity, and the time it took to understand what I had to do, it should be at least 4 kyu.

Great one.
I completely forgot regular expressions since school. :)

I think doing it right, and not the 5-6 line brute-force way, is a 4kyu task.

just imagine how much time and memory you need to use to count the length of a single [ 0 - 1 000 000 000 000] interval

Modified.
Why? Maybe because the name of the variable doesn't matter (?)

If you don't find two consecutive F(m) verifying F(m) * F(m+1) = prod you will return

[F(m), F(m+1), false] or {F(n), F(n+1), 0} or (F(n), F(n+1), False)

F(m) being the smallest one such as F(m) * F(m+1) > prod.

Why the change from n to m there?