All Lights (up to 20x20)
This activity belongs to the GeoGebra book Lights Out (Games with solutions).
Your goal is to turn off all the lights. The difficulty is that when you click on any square, in addition to its state, it changes the state of its adjacent squares.
You can expand the board up to 20 rows by 20 columns.
You can find more information about this game in this article (June 2002) of Suma magazine (Spanish magazine on the teaching and learning of mathematics).
Author of the construction of GeoGebra: Rafael Losada