(a) Hard sudoku puzzles are usually designed for defying our logical reasonings, so we can counter with the Principle of Least Choice (PLC) by selecting the least likely one when facing the multiple choices of our next move. The harder the puzzle, the more often PLC is recommended to be used; (b) This lecture serves as the preface for promoting the natural Sudoku (Sudoku with 17 givens). Accordingly, I plan to give a series of lectures, each containing two puzzles with illustrative solutions, the second one of which is the demonstration of the first of the 49 practice puzzles with annotated solutions. All natural Sudoku puzzles are downloaded from Gordon Royle list; (c) The minimum of 17 givens is required for a Sudoku puzzle to not having multiple solutions. There are no extra givens that puzzle makers can maneuver to design extremely hard Sudoku. Therefore, we shall not use PLC at all for any of our lectures; (d) The purpose of my lectures is for you not to waste time in playing Sudoku. In addition to the introduction of efficient methods, we most importantly screen out those puzzles with multiple or no solutions in the collection of practice sets for you; and (e)The lectures are presented in the power point format, convenient for any interested instructors to use.