I don't think "master" is as difficult as it's been described. In fact I found it much easier than expert. Finding a "key" row, filling in that, and continuing

I don't think "master" is as difficult as it's been described. In fact I found it much easier than expert. Finding a "key" row, filling in that, and continuing in a direct style was often the solution. I think this needs more depth to be a really good puzzle game, but it is on the right track.