with ten variations and a coda. Each variation is separated by "identical, basically decorative orchestral ritornelli". This movement is in 2/4 time until the end of the last variation, where 6 adagio bars in common time lead to a coda in 6/8 time. Authenticity Mozart is known through letters and concert announcements to have written a sinfonia concertante for flute, oboe, horn, and bassoon, the original score of which is lost. There is considerable debate about the authenticity of what is performed today, and whether the extant piece is even related to the original work. Various scholars have conflicting opinions, and some say the composition is currently in a corrupt form. Initially the Sinfonia Concertante seems to have been accepted uncritically as a slightly different version of Mozart's lost work. However in the 1930s Donald Tovey described it as "blundering" and "inept". Alfred Einstein however considered it genuine. He considered the work to be an arrangement which retained the essential nature of the original and he identified a recurring mozartean "motto" in the slow movement. Stanley Sadie was dismissive in particular noting that the solo clarinet cannot be directly back-transcribed to a supposed oboe part. Martin Staehelin considered that it was inconceivable that Mozart wrote a homotonal concerto (i.e. with all three movements in the same key; here E-flat major). No other attested Mozart concerto is homotonal though several of his symphonies and divertimenti are. Sadie thought that a sufficient reason for the homotonal character of the work might be to avoid a natural horn crook change and retune between movements. Staehelin has written a book about the work which argues that it cannot be by Mozart. The Mozart Project considers this piece as "spurious or doubtful", and it does not appear on the project's listing of concertos. Robert Levin analysed the Sinfonia Concertante and compared the structure of the work with known Mozart concertos. From this analysis he concluded that while the orchestral part and the first movement cadenza were spurious, the soloists' roles were based on the Mozart originals but had been modified by an unknown hand to substitute a clarinet for the oboe part and to change the flute for an oboe. This transcription process would have required the music for the three woodwind instruments to have been redistributed to accommodate the substitution of the clarinet for the original oboe part. Levin theorised that the unknown arranger