Sudoku Puzzles: Hard

150 sudoku puzzles, two to a page, with every solution included. The grids are 3.3 inches across in a 6 x 9 inch book — noticeably larger than a newspaper puzzle, and still small enough to carry. Every puzzle has exactly one solution, verified. Difficulty is graded by the solving techniques a puzzle actually requires, not guessed from the number of clues, so Hard means Hard for a solver's reasons.