Learning to play the piano is very common today and good pianists are so large in number that mediocrity is no longer tolerated at this instrument. As a consequence, one should study eight to ten years before one can risk playing a piece with a certain force, even among hobby musicians. But how few are actually able to dedicate so many years to the study of this instrument! And so it often happens that, due to insufficient practice, the performance sounds uneven and incorrect. The left hand gets...