Of course, when two people make music together today, we assume that they are equal partners. Bach was the first to hold it in this regard, as we do: his sonatas are a dialogue at eye level. The intimate partnership of a duo can certainly have a downside: When Posdnyschew, the main character in Leo Tolstoy’s novella “The Kreutzer Sonata”, gets presented by his wife and another man, the Beethoven’s work of the same name, he does not bear the intimacy of the two musicians and will to the murderer.