MLA

Schwartz, Delmore, 1913-1966. "Words for a Trumpet Chorale Celebrating the Autumn". Box 3, folder 212. 1961, undated. https://collections.library.yale.edu/catalog/17405251.

APA, 6th edition

Schwartz, Delmore, 1913-1966. (["Box 3, folder 212"])(1961, undated)["Words for a Trumpet Chorale Celebrating the Autumn"]. https://collections.library.yale.edu/catalog/17405251.