There's a large class of puzzles where a group of people, often described as perfect logicians, are put in a situation where they have to deduce things based on what they know, and what they know others know, and so on. Examples:

  • Blue-eyed islanders
  • Sum and product
  • Cheryl's Birthday
  • Some hat puzzles (not the team-strategy ones)

So far, only the blue-eyes puzzles have their own tag. I feel like there should be a tag that encompasses all of these, like or (I personally prefer the former). I'd of course go through and do the retagging.

Does anyone disagree with this? Or have opinions about the tag name?

  • $\begingroup$ Inductive knowledge? $\endgroup$
    – xnor
    Commented Jan 25, 2016 at 8:43
  • 3
    $\begingroup$ The mathematical term would perhaps be "Reasoning About Knowledge", which is much too long for a tag name; see mitpress.mit.edu/books/reasoning-about-knowledge . I like "common-knowledge". $\endgroup$
    – Gamow
    Commented Jan 25, 2016 at 11:21
  • 4
    $\begingroup$ @Gamow When I hear "common knowledge," I think "commonplace," as in, "stuff that everyone should know." Consider a sentence like, "It's common knowledge that you're only supposed to cross a street on a green light." Thus I think it's a poor choice for this context due to its likelihood of being misinterpreted. $\endgroup$ Commented Jan 25, 2016 at 18:00
  • 2
    $\begingroup$ Then shared-knowledge ? $\endgroup$
    – Ben Voigt
    Commented Jan 27, 2016 at 15:47

2 Answers 2


I think this is a great idea - the puzzle type is fairly common, and I'm surprised we don't already had a tag for it. As for the tag name itself, any of these would work well:

(Thanks to Gamow for the second one.)

  • $\begingroup$ Is there a reason you prefer meta-logic over meta-knowledge? $\endgroup$ Commented Feb 17, 2016 at 4:31

+1 for @BenVoigt's suggestion


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