MLA

Koch, Frederick R. (Frederick Robinson). Halévy, Ludovic. Box 20, folder 372. 1882-83, n.d.. https://collections.library.yale.edu/catalog/2007267.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 20, folder 372"])(1882-83, n.d.)[Halévy, Ludovic]. https://collections.library.yale.edu/catalog/2007267.