This revised edition was prepared by comparing the prior printed edition with the available manuscript sources, which are the following:1) a manuscript, apparently intended as a final copy, on deposit at the Szecheny Library in Budapest (998 Ms. Mus.), also published in facsimile by Editio Musica, Budapest,2) the manuscript that was the source of the first engraving by Universal Edition, apparently hand copied by the composer from the above, with a few minor alterations, 3) a printed copy corrected by Béla Bartók. (Peter Bartók, taken from the preface)