By Cuong Q. Nguyen
Last semester I posted a riddle regarded by a number of contemporary philosophers as the “hardest” logic puzzle in the world. Raymond Smullyan, a prominent logician and philosopher, has a number of logic puzzles available online for people to solve, and this particular puzzle received a lot of attention from our readers. After some considerable delay, here is both my solution and various other solutions to the puzzle. Enjoy!

By Cuong Q. Nguyen
Besides working on Prometheus, I like to distract myself from time to time trying to solve riddles and logic puzzles procured by philosophers. Raymond Smullyan, a prominent logician and philosopher, has a number of logic puzzles available online for people to solve. I’m proud to say that I solved a fair number of them but there’s this one particular puzzle by Smullyan that’s been coined by many philosophers to be “The hardest logic puzzle ever.” I found this early on in September 2008 and I’ve contemplated and quarreled with myself trying to solve this puzzle. Think you can solve it?