Step 3: Now remove all rows that are made completely of zeros. Because there are at most r entries different than zero in each column, the matrix now has at most r2 rows. We can test exhaustively all subsets of rows of size k of the first T 1 rows for domination of the now r2-th row. If none of the tests results in domi- nation, we have a no-instance, otherwise we have a yes-instance and a certificate of the domination.