Basic linear algebra allows us to set any 3x3 square to any value we want. Using this we can set the whole board to zero.

Full writeup: https://smyghalloumi.se/posts/2018-12-27-otw-advent-2018-playagame.html

Original writeup (https://smyghalloumi.se/posts/2018-12-27-otw-advent-2018-playagame.html).