MLA

Bacon, Leonard, 1887-1954. Frost, Robert. Box 23. 1939-1951. https://collections.library.yale.edu/catalog/17434886.

APA, 6th edition

Bacon, Leonard, 1887-1954. (["Box 23"])(1939-1951)[Frost, Robert]. https://collections.library.yale.edu/catalog/17434886.