Kv533 or K.533 are both the work numbers of Mozart’s Piano Sonata No. 15 in F major. K means that the editor of Mozart's music works, Kocher, used the initials of his name plus the work number as an important mark to distinguish Mozart's music works. Sometimes, the same work of Mozart will have two different numbers at the same time. This is because the work has been edited repeatedly, and both numbers have the same meaning.