I am wondering if this might be something universally known to the cognoscenti: In Laszlo Polgar's 5334 Chess Problems, number 638 seems to be given a wrong solution (638) 1.N×e6+ K×c3 2.Qd2#, ignoring 2....Kxb3; when the correct solution appears to be 1.Qe5, either K or Q x e5, 2. Ne2. It doesn't look like it could be a typo, because there are three non-nonsensical moves leading to a real pseudo-mate. I wonder if it could be a little trap to see if the reader is awake (or originally, if the three sisters were awake). Also, I should note that this is on a Chinese, likely non-official, download version, but which otherwise seems to be reliable. Another thing is, he doesn't really stick to the conventions of problem writing - not that I know anything much about those - doesn't exhaust all variations in analysis, doesn't bother about cooks. But this is a different thing. Just wondering if it's a thing he does from time to time, and everyone knows about it.