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The puzzle "Enigma" has been patented by Eldon Vaughn in teh United States in 1975. I have a version by Hanayama Toys which belongs to a Cast Puzzle series cured by Nob Yoshigahara. This is surely one of the hardest puzzles of this kind ever invented. I looked for information about the author but could only find that apparently the idea came to him in 1955 when he was only sixteen! 
Actually, I was able to solve it and put the pieces back together a few times though each time I was  just making many causal moves. It took me several days to find a solution which I include here in a sequence of shots for my own reference. I do not like particulaly the version I have because the pieces do not slide apart easily, but I have seen that there are other versions available for purchase in the internet. I do not know if the solution given here is the `correct one' as it is directly provided by some sellers.

Sometimes thinking about physics questions can be very stressing...

...go here and have fun with Calvin and Hobbes! The following strip has something related to my work on simultaneity

indeed essentially Calvin's dad uses here a definition of simultaneity based on the local position of the Sun. The holonomy of that simultaneity connection over a round trip of the Earth is a day (see my work). Calvin's dad tries to relate this holonomy to the effect of time dilation in special relativity! Good idea but it doesn't work! A puzzling effect of the one day holonomy of a simultaneity convention based on the position of the Sun was popularized by Jules Verne in his book Around the World in 80 Days.

Do you know the topological game Hex? It has very simple rules and has the very interesting property that no draws are possible. Download hexy.exe from here and have fun!