I’ve been playing with crossword puzzle variants. Here’s one that Dan A. will like. 1) The puzzle grid is an N by N torus. 2) In each row and column there should be exactly one black square. For example, here is a solved 7 by 7 puzzle (black -> blank): A D E R L E L E D S E A E R L E T T D W A N T E L A D D E R S E N D E R E A T E R H To avoid trivial solutions we should require that the horizontal words are not all the same — as in this one. Still, the solutions I’m finding all have lots of symmetry. Note that the vertical words in this solution match the horizontal words. Now here’s a challenge. Find a solution, with no repeated horizontal words, but where the black squares do not form a backward diagonal. -Veit