Commentary
The four sonatas “pour le clavecin...avec l’accompagnement de violon,” K. 6–7 and K. 8–9, were engraved in Paris as Mozart’s op. 1 and 2 in early 1764 (see also our entries for 5 Mar and 9 Apr 1764).
Michel Ferdinand d’Albert d’Ailly, Duc de Chaulnes (1714–1769), was an astronomer and physicist. The auction of his enormous library was held at his residence on the rue d’Enfer commencing on 19 Mar 1770.
The exemplar of the sale catalog in the Bodleian Library, Oxford (used for the Google Books scan) contains handwritten annotations against each entry that appear to indicate the sale price. The two Mozart prints were sold together with a set of sonatas by J. G. Lastig for one livre. "1765" and "1766" are catalog numbers.