I had a few ideas to create openings in this genre, when I had first thought of it. This puzzle uses one I hadn't put in before. It's much easier to put in than to spot. Although I made sure to at least mark it better than I had originally wanted to put it in. But the first time I showed someone the opening, they never found it till I pointed it out. So this is an easier variant of the opening. It's still a challenging puzzle, but I always enjoy playing around with this sudoku variation.