Logic Masters Deutschland e.V.

I'm so sorry. It had to be done.

Mad Fold-In is a new puzzle genre introduced by Gnubeutel and beautifully animated by OlliWright. Nebuzaradan and The Book Wyrm gave me helpful feedback regarding my wording of the rules, and I ended up borrowing heavily from the way gdc presents them. Special thanks to my dad for once again being my sounding board while I tried to justify some of the crazier logic to myself, and to Sotehr for fully testing an earlier version of this and (just about!) convincing me to add a couple of clues to smooth out the solve path a little!



Normal sudoku rules apply within the central 9x9 grid.

Mad Fold-In: The dashed red lines can be folded onto each other so that columns 1, 2, 8 and 9 form a 4x9 grid (i.e. columns 3-7 disappear).

Full Rank: In a 9x9 grid, a total of 36 nine-digit numbers can be read in the rows and columns, each viewed from both directions. If these are listed in ascending order, a "full rank clue" indicates the position in this list of the nine-digit number seen from the clue, where a "1" clue would indicated the lowest nine-digit number and a "36" clue would indicate the highest. In a 4x9 grid, a similar list can be made with 26 entries, 18 of which have four digits.

Full Rank Differences: A clue outside the grid in this puzzle shows the DIFFERENCE between the value of the full rank clue in that location as it would appear in the 9x9 grid and the value of the full rank clue in that location as it would appear in the folded 4x9 grid.

(Clarifications: There are no tied ranks, i.e. identical rows/columns, even in the 4x9 grid. Differences are absolute, i.e. if the value of a full rank clue for the 9x9 minus the value for the 4x9 grid is negative, the clue displayed will still be positive. The outer cells have been provided for note-taking purposes only.)