On Thu, Mar 26, 2015 at 8:23 AM, Marko Rauhamaa <ma...@pacujo.net> wrote: > Ian Kelly <ian.g.ke...@gmail.com>: > >> I don't think that I have used trial and error, in my head or >> otherwise, in any sudoku I have ever solved. > > Of course you have. "This here can't be a 2 because if it were a 2, that > there would have to be a 5, which is impossible. Thus, the only > remaining alternative is 3, so I mark that down." > > That's trial and error, aka, reductio ad absurdum. > > (Additionally, sudoku solvers are known to pencil all kinds of markings > on the sudoku sheets to help the deduction work.)
Okay, I've probably used single-lookahead trial and error in my reasoning at some point. But the example you give is equivalent to the deductive process "That can't be a 5, so I remove it as a candidate. The only place left for a 5 is here, so I remove the 2 as a candidate and fill in the 5." -- https://mail.python.org/mailman/listinfo/python-list
