/prog/ challenge #8489929

Create a list of /prog/ challenges. A /prog/ challenge should satisfy the following criteria:

1. It should be completable within 5 - 10 minutes by an EXPERT PROGRAMMER.

2. It should be completable within 5 - 10 days by a non-expert programmer.

3. A non expert programmer should become closer to an EXPERT PROGRAMMER after completing the challenge.

4. The challenge should stimulate interesting conversation, or perhaps elude to more interesting and fundamental problems.

>>7
Prove that there is a "success".
Verify your proofs. Prove that the proofs prove what they were intended to prove, and verify the correctness of this proof.
Only then will there be any success to speak of.