The original X-Sums rule, that forms the basis of this genre, can be traced back to the SUDOKU 8X8 LMI contest, by Zuzanahromcová & MatúšDemiger. This was followed shortly by two addtitional puzzles: one by Bram de Laat and another by Richard Stolk.
In 2020, Jonas Gleim made a X-Sums puzzle for the Puzzle Alphabet competition, which is likely the first standalone X-Sums puzzle.
In 2022, dohz formed the first full X-Sums puzzle set. Inspired by this classic set, Pedro added arrows plus some extra cursed puzzles, while creating this interactive app (2023), using the Kudamono Editor.
Each puzzle has a single, unique solution.
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This small example by PinkHoodie clarifies the behaviour of absent cells:
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This series uses empty arrows inside the board, thereby giving no number clue away. It can be considered a small cursed expansion to the original, classic ruleset, which did not bar this possibility.
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zero
The zero variant was first used in a standalone X-Sums puzzle by Jeffrey Bardon (IHNN).
Here's a set of puzzles by dohz using this variant:
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And a puzzle by PinkHoodie:
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kropki,clues-missing
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antiknight
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Acknowledgements and Changes
2023-04-13 Extensive thanks to dohz for transcribing the classic set (and adding a new puzzle!), for thoroughly checking the cursed set!
2023-04-15 Thanks to dohz for making this page and implementation tremendously better!
2023-04-16 Thanks to Freddie Hand (Puzzle Maestro), Jonas Gleim , Lennard Sprong (X_Sheep), Martin Ender (Menderbug), David Altizio (djmathman), Jeffrey Bardon (IHNN), Tom Collyer for help tracing and understanding the elusive origins of this genre.
2023-11-04 Fixed a regression found by dohz (cause: incorrectly set mode at startup)
2023-11-05 Restored correct grid/frame drawing (external lines no longer shown); added slightly better hotkeys for arrows
2024-01-20 Variant zero added to X-sums
2024-01-23 dohz transcribed 4 puzzles using the newly implemented zero variant! Thank you.
2024-01-30 Puzzle Mirror match by dohz was updated to a stronger version
2024-01-12 X-Sums error style updgraded alongside that of Hit Points
2024-03-10 A cursed puzzle was sent by 5381 - thank you!
2024-03-19 PinkHoodie modernised the rule panels for X-Sums, a tricky task. Thank you!
2024-05-24 The particular case of kropki clues outside the grid is now supported, for an X-sums puzzle by PinkHoodie.
2024-05-24 puzzletters PinkHoodie sent 2 puzzles using variants kropki,clues-missing and zero!
2024-06-03 The antiknight variant now considers only inside numbers, as highlighted by PinkHoodie by sending a great test case, and a puzzle!
2025-01-14 External arrows became optional in X-Sums, when axis-aligned, following the global convention for all genres. Highlighting style updated accordingly.
2025-02-10 A small example by PinkHoodie clarifying the behaviour of absent tiles was added - thank you!
2025-03-01 A bug in the external clue range reported by PinkHoodie was patched. Also, PinkHoodie recently re-added missing arrows to the variant puzzles.
2025-04-26 Questions temporarily removed from X-Sums - apologies for the inconvenience