Heinrich Schenker and Beethoven's 'Hammerklavier' Sonata

In 1912 Heinrich Schenker contracted with the Viennese publisher Universal Edition to provide an 'elucidatory edition' (Erl erungsausgabe) of Beethoven's last five piano sonatas. Each publication would comprise a score, newly edited by Schenker and using the composer's autograph manuscript as principal source, together with a substantial commentary combining analytical, text-critical and performance-related matter. Four of the five editions appeared between 1913 and 1921, but that of the 'Hammer