Normal sudoku rules apply. A digit in row 1 indicates which row contains the 1 in that column. Eg if r1c4 was a 6 then 1 would appear in r6c4. A digit in row 9 indicates which row contains the 9 in that column. A digit in column 1 indicates which column contains the 1 in that row. Eg if r7c1 was a 4 then 1 would appear in r7c4. A digit in column 9 indicates which column contains the 9 in that row. Clues outside the grid indicate the sum, or parity of the sum, of the digits sandwiched between the 1 and 9 in their rows/columns.