Which 2 is wrong? The 2 in position 5 is wrong and needs to be changed to a. Also this is not allowed, as we need to fill in the numbers 1 to 6 once in each row, column and region. Numbers may only appear once in each column. This is not allowed! The first one (in position 3) is wrong and should be a. In this example we have 2 ones in the first row. The numbers 1 to 6 must be filled in each row and column once. In whatever format are divided in rows, colums and regions (marked by a thick black line).
Numbers may only appear once in each row.
