Upon reading the first few pages and seeing the pictures I realized that all Tetris pieces are made of shapes with 4 adjacent cells. Additionally, all permutati

Upon reading the first few pages and seeing the pictures I realized that all Tetris pieces are made of shapes with 4 adjacent cells. Additionally, all permutations of 4-cell shapes are represented in Tetris. It also clicked that the prefix is similar to tetra. I suspect many other folks realized this already but it was a charming lightbulb moment for myself.