From Rineke Verbrugge:

In the summer of 1984, I was a young math student, wanting to do something with my hands over summer and fascinated by the countries behind the Iron Curtain. So I traveled to Czechoslovakia, to dig ditches and clean parks in an international youth workcamp. I struck up a friendship with a Czech student of medicine, Jarda Kučera. At a certain moment we were working, just the two of us, in a remote part of the castle grounds, so we had an opportunity to discuss the political situation in Czechoslovakia - one always had to be careful because some Czech participants might be informers for the Secret Police.

Jarda told me that he had heard that the famous dissident Václav Havel had written a booklet in samizdat (the underground press), and he recommended me to find it when I would be back in Holland. It was called "The anatomy of a reticence":
http://archive.vaclavhavel-library.org/kvh_search/Functions/show_thumbnail.php?id=7287

After the holidays, Jarda and I started writing each other letters. We wrote about innocent topics, for example, my attempts at learning Czech, because it was common knowledge in the early 1980s that the secret police opened and read the correspondence between the East and the West. After a few months, Jarda wrote a whole paragraph about his anatomy course and his anatomy book in his letter. I wondered a bit why he was going on about that to me, a math student. But then there was the sentence: "How do you find your anatomy book?". My heart skipped a beat: how courageous, how clever! I followed the hidden protocol and answered in kind about the eye-opening anatomy book. In his next letter, Jarda asked me to bring the anatomy book on my next summer trip to Prague, for him to have a look. So in the summer of 1985, I hid the pamphlet in my luggage and spent some sweaty hours in the train at the border when the guards came in. My luggage was not searched and everything ended well...

Now, thirty years later, together with
Hans van Ditmarsch, Sujata Ghosh and Yanjing Wang, we have written an article that investigates just this kind of "hidden protocol". Today, I received the announcement that our article "Hidden protocols: Modifying our expectations in an evolving world" has been published in the March 2014 issue of the journal Artificial Intelligence: http://www.sciencedirect.com/science/article/pii/S000437021300129X?np=y

In the article, we introduce an extension of dynamic epistemic logic to formalize the fact that after certain announcements, some listeners who are "insiders" on the hidden protocol know exactly what's meant by the speaker, while other listeners may not have the faintest clue.

The technical parts of the article presuppose quite a bit of prerequisite knowledge on logic, but the examples ("the voice of Kathleen Ferrier", "Valentine's Day", "Dutch or not Dutch" and "hundred prisoners and a light-bulb") are meant to be understandable by a wider audience. Looking forward to your comments!