There are some nice puzzles there. There is some overlap between my favourite puzzle page, by Rustan Leino: <a href="http://research.microsoft.com/en-us/um/people/leino/puzzles.html" rel="nofollow">http://research.microsoft.com/en-us/um/people/leino/puzzles....</a>, but both have a number of puzzles the other doesn't.<p>Edit: corrected Leino's name.