My last post was about “Cheryl’s birthday puzzle”, which recently became an internet sensation. I mentioned several additional puzzles in that post and promised solutions; here they are.

Let me begin, though, with a “cryptography” variant of the Cheryl puzzle which was sent to me by my friend and puzzle guru Pete Winkler:

Cheryl’s birthday possibilities are now May 14 or 15, June 15 or 16, July 16 or 17 or August 14 or 17. Albert gets the month and Bernard the day as before, and they both want to find out the birthday. But Eve, who’s listening in, mustn’t find out. How can A and B, who’ve never met before (and aren’t cryptographers), accomplish this mission?

Think about it, it’s a fun little puzzle! [Pete writes in addition: “You can also do this with a cycle of 5 months (10 dates total) but then you need a coin to flip.”]

My *Meta-Cheryl Challenge* (as revised on April 20) was to come up with a list of dates for which the following puzzle will have a unique solution:

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