Sudoku ST

Sudoku where the difficulty label is a promise rather than a guess. Every puzzle is graded by the solving technique it actually requires, and every one can be finished by reasoning alone. If the solver cannot complete a puzzle with logic, it is rejected instead of shipped with a label it cannot honour. FIVE BANDS THAT MEAN SOMETHING Easy asks for singles only — every step has a cell you can finish outright. Medium adds locked candidates: a digit trapped in one line of a box. Hard brings pairs and triples — cells that share their options. Expert needs a board-spanning move: an X-wing, a swordfish, a chain of colour. Master needs several of them and long reasoning, but never a guess. BUILT FOR THINKING • Pencil marks, with notes that clear themselves when a digit makes them impossible • Duplicates, matching digits, and the row, column and box you are working in, all highlighted — and each…