I've seen this article every now and then, and it's always fun to read. Something jumped out at me this time, though:
> As computer security expert Ben Laurie has stated, Sudoku is "a denial of service attack on human intellect". Several people I know (including my wife) were infected by the virus, and I thought maybe this would demonstrate that they didn't need to spend any more time on Sudoku.
Ah, yes... remember the halcyon days of 2006, when something as benign as Sudoku was considered to be a "denial of service attack on human intellect"?
It was a denial of service attack, not in the sense of soaking up my brain cells solving puzzles, but in causing me to devise and program my own solver. (In Java, text console only.) Once I wrote a solver, I felt as if I had solved all puzzles.
Then I got interested in devising puzzles with multiple solutions. Not too difficult. But making a few puzzles with two solutions was fun.
Experiment_203(
" 1 . . | 2 . 8 | . . 9 "+
" . 8 . | . . . | . 3 . "+
" . . 7 | . 1 . | 2 . . "+
//------+-------+--------
" 4 . . | 1 2 3 | . . 6 "+
" . . 2 | 4 5 6 | 9 . . "+
" 6 . . | 7 8 9 | . . 4 "+
//------+-------+--------
" . . 6 | . 4 . | 8 . . "+
" . 2 . | . . . | . 7 . "+
" 9 . . | 8 . 2 | . . 1 "
),
// 245 boards examined so far.
1 6 5 | 2 3 8 | 7 4 9
2 8 4 | 6 9 7 | 1 3 5
3 9 7 | 5 1 4 | 2 6 8
------+-------+------
4 7 9 | 1 2 3 | 5 8 6
8 3 2 | 4 5 6 | 9 1 7
6 5 1 | 7 8 9 | 3 2 4
------+-------+------
7 1 6 | 3 4 5 | 8 9 2
5 2 8 | 9 6 1 | 4 7 3
9 4 3 | 8 7 2 | 6 5 1
// 287 boards examined so far.
1 6 5 | 2 3 8 | 7 4 9
2 8 4 | 9 6 7 | 1 3 5 // <-- 9 6 7 instead of 6 9 7
3 9 7 | 5 1 4 | 2 6 8
------+-------+------
4 7 9 | 1 2 3 | 5 8 6
8 3 2 | 4 5 6 | 9 1 7
6 5 1 | 7 8 9 | 3 2 4
------+-------+------
7 1 6 | 3 4 5 | 8 9 2
5 2 8 | 6 9 1 | 4 7 3 // <-- 6 9 1 instead of 9 6 1
9 4 3 | 8 7 2 | 6 5 1
2 total solutions found.
304 total boards examined.
Total time 0 days 00:00:00.041.
Solution #1. Found in 0 days 00:00:00.029.
3,906 boards examined so far.
1 total solutions found.
7,832 total boards examined.
Total time 0 days 00:00:00.085.
Found this explicit rejection of the Robustness principle[1] fascinating. It comes after decades of cURL operating in the environment that was an ostensible poster child for the benefits of the principle--i.e., HTML over HTTP.
[1] https://en.wikipedia.org/wiki/Robustness_principle
Better advice is to not do something unexpected -- even if that unexpected result is clearly documented, but someone did not read it.