This is part 1 in a series of related puzzles. You can see all the puzzles in this series on my website at kammer.xyz/blog/sudoku/photocopied.
You can also visit the logic-masters pages for the other puzzles in the series:
You have been gifted a large collection of puzzles from a friend. You sift through them looking for interesting ones and find photocopies of puzzles from an old book of puzzles, filed under "puzzles with no given digits". The original book is nowhere to be found and the photocopies are in black and white.
You can see the original photocopies on the webpage linked above, but the images are too large to upload here
You assume the original had a unique solution, but can you still reconstruct that solution? The rules below are listed for the entire section of puzzles, so you can't be sure whether all three line types actually exist in any of the puzzles.
Your goal is to figure out what the original solution to each puzzle was. I have transcribed the puzzles and put them on sudokupad for your ease of solving!
This 4x4 will likely provide a hint on how to solve the next puzzles. If you want to challenge yourself, try the other ones first. If you can't make any progress, return to this one for a little hint.
Solution code: Bottom row, left to right
on 31. July 2026, 02:28 by gkammer
I still got comments saying the rules weren't explicit enough. I'm sorry to anyone who got frustrated with this puzzle -- I personally found the metapuzzle aspect of the implicit assumption interesting and novel, but it seems the puzzle solving community found it unrigorous and bad form. I really hope I've made it sufficiently explicit now, but feel free to keep letting me know if you disagree.
on 25. July 2026, 19:41 by gkammer
Following some constructive criticism in the comment, I've edited the puzzle text slightly to be more explicit about a particular important rule that was previously implicitly assumed.
on 23. July 2026, 18:41 by barnacle
Very clever! Joy in doing it.
on 23. July 2026, 15:38 by XhcnoirX
It took me a second but I understand what you mean with 'original coloring' now. Clever!
on 22. July 2026, 23:14 by gkammer
Solvers have mentioned that they think there are multiple valid solutions to this puzzle. I am once again confirming that I am 100% confident there is only one valid solution. If you think there are multiple, please reread all of the backstory, rules, and the second setter's note -- you are missing something!