Ok, probably to a mathematician these are not arcane, but to normal people (oops, sorry, I love mathematicians) I think they might be. Anyway, read and enjoy without any further commentary:

- Needle-in-a-haystack Problems: "[snip...]A needle-in-a-haystack problem is a problem where the right answer is very difficult to determine in advance, but it's easy to recognize the right answer if someone points it out to you. Faced with a big haystack, it's hard to find the needle; but if someone tells you where the needle is, it's easy to verify that they're right[snip...]"
- Needle-in-a-haystack Problems, and P vs. NP. "[snip...]Last week I wrote about needle-in-a-haystack problems, in which it's hard to find the solution but if somebody tells you the solution it's easy to verify. A commenter asked whether such problems are related tothe P vs. NP problem, which is the most important unsolved problem in theoretical computer science. It turns out that they are related, and that needle-in-a-haystack problems are a nice framework for explaining the P vs. NP problem, which few non-experts seem to understand.[snip...]"