Sudoku looks like a number puzzle, but underneath it is pure mathematics: constraints, symmetry, and counting on a scale that is hard to imagine. Try both labs below.
Every row, every column, and every 2×3 box must contain the numbers 1 through 6 exactly once. Tap an empty cell, then tap a number. Watch what happens when a number repeats where it should not.
Start with one valid, completed grid. Each button below applies a transformation that mathematicians call a "validity preserving symmetry." No matter how many times you press, the result is still a perfectly valid Sudoku.