As mentioned below, don't put crucial testing function in Preloaded. Migrating them to test fixture is trivial, and saves from all kinds of shenanigans.

Approved! :)

After 140 code submission one jakber provided an actual solution (other 3 smart guys managed to cheat on my initial easy test fixture).
Since jakber is 2kyu, I think that this kata should be 2kyu, too.
What do you think?

Thank you, this is a good idea.
I update the description in order to match the Christmas theme better.

I randomized the test fixture better. Now it should be almost impossible to cheat the test.
I also added some sample fixture to help user test their code.

Hi,
thank for your suggestions. I added some randomness on x values, I'll add some randomness on functions as well so that you're cheat will no longer be a solutions.

Typo corrected.

Ciao,
s

Hi,
I updated the test so that if you exceed the max number of calls to h it now shows you the value x that you where supposed to compute and the calls limit.

It seems that this one is quite difficult... only one person managed to solve it in 2 hours and a half (out of more than 50 code submissions). But believe me, it is just 10 lines of code... you just have to think a little bit out of the box.
C'mon guys!

Ciao,
Saverio.