Quads are much rarer, plus they’re considerably less handy in a method since they don’t Allow you to slim down numerous candidates abruptly, but when you see 1, it’s well worth investigating. Fixing single squares may convert quads into triples or pairs, so don’t ignore these! ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​... https://sudokuhard-hardsudoku00108.bloggadores.com/26478669/the-greatest-guide-to-sudoku-hard-hard-sudoku