Vice versa for C who, as it is known, can see that B has blue eyes. No one knows the color of their eyes. Is it really known who was the first to come up with it (in any form). The genre of public, published puzzling was arguably pioneered by.I'd like io9's Sunday Puzzles to follow a similar format to Tierney's, and for the comments to become a place for people to submit full or partial solutions, questions, ideas, future puzzles, and so on. Finally, D thinks that C might think that B might think that A might not see anybody with blue eyes.Why do they have to wait 99 nights if, on the first 98 or so of these nights, they're simply verifying something that they already know?Each night gives them additional knowledge about other people's knowledge. Its universal knowledge that there is at least one person with blue eyes. They don't know their own eye color, so they think that they may have blue eyes. Why is considering the 1 and 2 blue eyed person cases relevant?Each day, you prove the n+1 case to be common knowledge. (In retrospect, it was the obvious thing to think about. Blue Eyes: The Hardest Logic Puzzle in the World. Of the 200 islanders, 100 have blue eyes, and 100 have brown eyes. How, then, is considering the 1 and 2-person cases relevant, if they can all rule them out immediately as possibilities?With four people, A, B, C & D, imagine D sees three people with blue eyes. Now consider if there were two-blue eyed people.It would also help to stress that there is a ferry every day, and the question is not just about the first day.From the start of time to day -1, it is [universal knowledge](.This distinction is the answer to followup question 1, if you didn't at least click the links and skim through the first paragraph, you will probably be confused at what I'm about to say. The underlying strategy is this: if it's the 100th day, and you see only 99 other people with blue eyes, you must have blue eyes. Then they all know there's more than 98 blue-eyed people, and so they are themselves blue-eyed.This explanation has been the easiest for me to wrap my head around.I'm not even sure why this needs the guru since everyone can see for themselves that some people have blue eyes.Thats the whole point of the puzzle.
Until the guru talks, you don't know that the other person knows that. There's no guessing or lying or discussion by or between dragons. I'm still sorting out the details (I like to think that our commenting system has the potential to be moderated in a way that will foster discussion and help people along in the puzzle-solving process, without always spoiling the solution outright – but how feasible this will be in practice remains to be seen), so recommendations on how to structure the column are of course welcomed and encouraged.There's so much more I could say about this, but I'll refrain for now (or reserve it for future posts), save for one last thing:Alright. They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. The answer does not involve Mendelian genetics, or sign language. I will give you this example to make it a little bit simpler. The site may not work properly if you don't,If you do not update your browser, we suggest you visit,Press J to jump to the feed. But if they haven't left, then each of them saw 99 other people with blue eyes, which must include you.The only way to know useful information is whether or not people left. The link at xkcd says: I didn't come up with the idea of this puzzle, but I've written and rewritten it over the the years to try to make a definitive version. Standing before the islanders, she says the following:Who leaves the island, and on what night?There are no mirrors or reflecting surfaces, nothing dumb. But its basically something like if you can prove that an arbitrary first case is true (that 1 person will leave after 1 day) and that if n is true then the n+1 case is also true you've essentially proven that the solution is valid for any number of n higher than the initial value. They can’t escape, but there is one strange rule governing their captivity. They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. How would the guru know that her eyes are green not purple?If these are all logical people doing logical things, wouldn’t they just ask “What color is my eyes” and everybody leaves on Day 1?The correct answer seems to have to be that no one leaves. The guru says “i see a person with red eyes.” You expect the red eyed person to look around and see all blue eyed and brown eyed people, figure out he’s the one with red eyes, and leave on night one. The puzzle is fundamentally identical to Green-Eyed Dragons, but Munroe's version includes some wording that provides what I think is a fairly big clue, so if you find yourself struggling with the dragons,I will make the same closing points here that Munroe does: This is not a trick question. If you already knew what the difference was, you would've figured out the puzzle on your own.what is the quantified piece of evidence the guru provides?The guru makes it common knowledge when before it was just universal knowledge. No one knows the color of their eyes.