fact: Definition sudoku l := length l = size * size /\ (forall i, i < size -> Permutation (row i l) ref_list) /\ (forall i, i < size -> Permutation (column i l) ref_list) /\ (forall i, i < size -> Permutation (rect i l) ref_list).
imports: List UList Permutation Div OrderedList ListOp Lia