MLA

Ernest Augustus, King of Hanover, 1771-1851. Der Freischütz.... Arranged Carl Zulehner. Vocal score. Print (Mainz: B. Schott Söhne). Box 144, folder 765. 1820s?. https://collections.library.yale.edu/catalog/10000214.

APA, 6th edition

Ernest Augustus, King of Hanover, 1771-1851. (["Box 144, folder 765"])(1820s?)[Der Freischütz.... Arranged Carl Zulehner. Vocal score. Print (Mainz: B. Schott Söhne)]. https://collections.library.yale.edu/catalog/10000214.