I'm thoroughly impressed by your geometric abilities! I didn't know that, and took me a while to check. Any hints on the puzzle, and as a sidequestion, what tools do you use to figure this kind of question? Just imagination, vector algebra, elementary trigonometry?
Huh? There's nothing to be impressed about. You can stick a tetrahedron inside a cube so it creates the same square shadows in all three directions: https://i.stack.imgur.com/oAUnH.gif
I know a lot of math, but for this puzzle, drawing stuff on paper is enough. Here's a hint: if you cut off one corner of the cube, all shadows are still square. How much can you cut? Can you cut some corners strategically to make at least one new square shadow while keeping all the old ones? How many square shadows can you get?
Could it help to have a point-like light source from a good angle that gives you a sharp shadow? Then it may be possible to judge distance based on the distance between the tip and its shadow.
I feel the pagination method demonstrated here is advantageous in that regard, eliminating vertical motion while allowing to see parts of two "pages" at the same time:
I would love to have that on my ebook reader, may need to hack that together some time to try. I dislike switching back and forth between two pages as is sometimes necessary; in this regard, this even seems better to me than a regular book.
Or possibly the other way round? 0hh1.com was registered in 2014 according to whois info, the puzzles on this site go back to 2011. (I'm not claiming this is proof, of course)
They're older than that, this kind of puzzle is called a Takuzu or Binairo and was invented in 2009 by a pair of Belgians: https://fr.wikipedia.org/wiki/Takuzu
Why "problematic"? The Al Viro change mentioned in the fix is https://github.com/torvalds/linux/commit/227158db160449b6513.... The commit says this makes the bug not exploitable since the new helper function handles correctly the edge case. The fix still needs to be applied to avoid computing the checksum twice.
