Since we only would be able to quote the famous problem by Smullyan, which is a rework of a previous problem, we instead asked the retro chess expert Andrew Buchanan for a short statement, which is reproduced in full below:
"I am in touch with the NY logicians group that Smullyan belonged to. I enjoyed speaking with him by phone, but never met him face to face alas. I admired his simplifying approach to logic, which led naturally to his popularisation work. My favourite is "To Mock a Mockingbird" (1985) - a beautiful exploration of combinatory logic. There is no book like it. Another highly original book was the delightful "Chess Mysteries of Sherlock Holmes" (1980) an introductory to chess retrograde analysis, in the form of solutions conducted by the great detective to his Boswell. The challenge he implicitly leaves to us chess problemists is how, in an age where the game itself has great popularity, we can successfully communicate the delights of the compositional world, and grow the next generation of composers and solvers from the grass roots up."
EDIT, 16 Fabruary 2017: Minor correction.
