Inside Sudoku first appeared on the US Sudoku Qualification. I thought the idea worked pretty well. I don't remember seeing it anywhere after that. I turned the idea in a Frame Sudoku, which has been repeated numerously, mostly by Richard Stolk.
The construction of the combination took a bit of work. Setting up the opening was pretty easy, but after that it gets a lot trickier. It's hard to pick the right digits that help both puzzles along. I liked the opening and found some points that nicely helped both puzzles along. It was hard to find a way to get both puzzles unique. There were a few situations that wouldn't resolve uniquely and I took a while to figure out how to avoid those.
I think both puzzles turned out nicely. The Outside Sudoku is the easier of the two. You get a lot of simple digits from the opening, while the Inside Sudoku's opening is more of a struggle. Enjoy.
Rules for Sudoku
Inside Sudoku: In this Sudoku digits on the outside indicate that these digits must appear in the 2nd, 3rd or 4th cell in that row or column when looking from that side.
Outside Sudoku: In this Sudoku digits on the outside indicate that these digits must appear in the first three cells in that row or column, when looking from that side.
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