Anti-Quadruples

What is the Anti-Quadruples rule?

Anti-Quadruples is a variant sudoku rule: the digits in a circle at the corner of four cells must NOT appear in any of the cells touching it.

In every puzzle here the setter’s own rules text is shown beside the board, so the exact wording for the puzzle you are solving is always one glance away. All normal sudoku rules apply unless the setter says otherwise.