This is the first book by Djape with classic Sudoku puzzles.
There are 5 difficulty levels with 60 puzzles each. First 240 puzzles can be solved by using standard Sudoku solving methods: naked or hidden singles, pairs, triplets and quads, and row/column and box interactions.
The final level, the so called INSANE, contains puzzles which require you to use either the X-Wing or Swordfish techniques. How they're used is explained in the introduction.
There are no trivial puzzles in this book - even those in the COOL category can be tricky. So, sharpen your pencils and have fun