Sudoku

The principle that allows a Sudoku puzzle to be solved can be understood easily. Simply fill a 9x9 square that contains nine further subsquares each of 3x3 with the numbers 1 - > 9 without the same number appearing in the horizontal or vertical aligned with it or in the same subsquare. The logic used to solve these puzzles, however, is not so straightforward.

The inverted pyramid can be illustrated using the Sudoku principle. If a solution is faltering it is sometimes obvious, but can result in an almost 'completed' puzzle that fails literally at the last square when it is discovered that a number is not unique to the line or subsquare. Disaster. The traditional Sudoku puzzle is small enough to start again and in most cases will enable a puzzle to be solved, but only by starting again. The 'mistake' can sometimes be identified, but often this just results in shifting the problem elsewhere. A total solution remains elusive.

Clearly a large physical project cannot be dismantled so easily.