Programming, Binary Decision Diagrams, Computer Science, Boolean.
function. Let the variable x_{i, j, k} = 1 if the digit k is chosen for the box at row i, column j in the grid and 0 otherwise. For example, for the solved puzzle above x_{3, 2, 9} = 1 because 9 appears at the spot (3, 2) on the grid. Since i, j, and k all range from 1 to 9, there will be 9³ = 729