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This is not a bad concept, but I agree with crsunlimited that the game verifier is goofy; when I gave a 20x20 puzzle a try, I started the way I had started on the 10x10 - the sides - but then ran into a situation where none of the ways to make sensibly divided shapes seemed to result in suitable confinement according to the game. Irritating as hell and makes me want to just spam walls all over the place instead of try to play properly.
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Full explanation of the verifer problem I'm having - it doesn't tell you if you're *missing* walls, only if the walls you have up aren't correct. Add + to get a fix for this.