Sudoku U: PhD in Sudoku

We'll school you in sudoku! Find your grade, improve your play-and graduate to the next level.
Sudoku professor Frank Longo has crafted five books with 300 sudoku each, which will take students from solving basics to super-hard, super-expert strategies. Try them and see how far you can go!

Warning: these excruciatingly hard puzzles are for sudoku experts only! In order to solve these brain-busting conundrums, you must master not only one upper-level technique, but an array of skills. Every one is a challenge.