Normal sudoku rules apply. Draw 9 straight diagonal lines, each through the centres of at least 3 cells: Every line contains exactly one Bull and one Red Flag; Different lines do not cross or share cells; The grid is a torus, i.e. row 1 wraps around to row 9 and column 1 wraps around to column 9 as shown. No two Bulls contain the same digit; The digit on a Bull is the average (mean) of all digits on its line. No two Red Flags contain the same digit; The digit on a Red Flag is friendly, i.e. it equals its own row, column or box number (rows, columns and boxes are numbered 1-9 from top to bottom, left to right, and in reading order respectively).