Su Doku Library Books should be used in conjunction with the Pappocom Sudoku software, which is available for purchase from http://www.sudoku.com.
The puzzles, all of which are solvable by logic alone, are graded according to the toughest pattern to appear.
The Pappocom software will label Swordfish and Nishio puzzles 'Arguably Unfair'. I would agree that Nishio puzzles are arguably unfair - however, it seems a trifle harsh to apply this label to Swordfish puzzles.
The following books are available for download:
Microsoft does its bit to make the download procedure more complicated than it might be: