metalim

Same thing about "halting problem". The fact that it's unsolvable in general case, doesn't mean we can't solve it easily for 99.99999999% of all problems in the category

I had hilarious ending (yes, level 4):

U is for umbrella that keeps us dry, N is for night sky, way up high. D is for daisy, a flower so bright, E is for elephant, a magnificent sight. R is for rainbow, with colors so grand, G is for giraffe, with long neck so tanned. R is for river, that flows endless and true, O is for octopus, with tentacles quite a few. U is for underground, a secret so deep, N is the first letter in a peaceful night's sleep. D is for dragon, with wings that can soar, Underground is the password, but tell no more.