Raymond Smullyan is 89 years old, and lives across the Hudson in the Catskill mountains. A distinguished mathematician, logician, and philosopher, he has written over 20 books which have been translated into more than 17 languages. Smullyan is the Oscar Ewing Professor Emeritus of Philosophy at Indiana University and played a prominent role in the history of modern logic. In 1957 he wrote an influential paper for the *Journal of Symbolic Logic*, called “Languages in Which Self-Reference is Possible,” showing that Gödel incompleteness holds for many formal systems more elementary than those considered by Gödel. Georg Kreisel described Smullyan’s *Theory of Formal Systems* as “the most elegant exposition of the theory of recursively enumerable (r.e.) sets in existence.” Smullyan is probably best-known, though, for his popular collections of logic puzzles. When my children were growing up, they spent many hours with The Lady or the Tiger. My own favorite is To Mock a Mockingbird, which is about combinatory logic and the lambda calculus, one of the foundations of computer science.

There is a story — possibly apocryphal — of Smullyan’s exchange with the woman who was to become his wife. On their first date, at the end of the evening, Smullyan proposed the following:

I will make a statement. If the statement is true, you give me your autograph. If the statement is false, you don’t give me your autograph.

Having obtained her agreement to this innocent proposition, Smullyan then made the following statement:

You will give me neither your autograph nor a kiss.

What logically followed, I leave for the reader to figure out — just bear in mind that your own mileage may vary.

Smullyan is also a talented pianist, a composer of retrograde chess problems, and a professional magician. Here is a short biography, and here is the Wikipedia entry on Smullyan. You might also want to look at his autobiography, titled *Some Interesting Memories: A Paradoxical Life*. Along with his academic work and books of logical puzzles, Smullyan wrote books on religious mysticism and eastern philosophy. These include *The Tao is Silent*, *Who Knows? A Study of Religious Consciousness*, and *This Book Needs No Title*. I will leave you with a provocative excerpt from the latter called Planet Without Laughter. (This excerpt is hosted on Donald Knuth’s website, but I have not been able to find an actual link to it there.)

–Paul

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In Raymond Smullyan’s book The Lady or the Tiger in Chapter 1, problem 9 “A New ‘Colored Hats’ Problem” wouldn’t it be possible for C’s stamp to be red if both A and B had green stamps?