Oh, almost over: Cheryl's Birthday ( https://en.wikipedia.org/wiki/Cheryl's_Birthday )
Text for that wiki page: Albert: I don't know when Cheryl's birthday is, but I know that Bernard doesn't know too. Bernard: At first I don't know when Cheryl's birthday is, but I know now. Albert: Then I also know when Cheryl's birthday is. My question: Have you examples where expressing "I don't know" was part of the solution? Groeten Geert Stappers -- Silence is hard to parse
