Something this illustrates, though - once you solve a problem, read the forum thread (the link will be at the bottom of the problem page when solved). I learne

Something this illustrates, though - once you solve a problem, read the forum thread (the link will be at the bottom of the problem page when solved). I learned so much poring over the solutions of earlier solvers. Without that knowledge, there's no way I could have gotten lots of later problems. Sure, problem #15 is very early and I happened to know the answer right off, back the first day I started solving PE problems. But even so, there are some gems in the posts from other solvers.