MLA

Williams, William Carlos, 1883-1963. Creeley, Robert. Box 4, folder 145-146. 1950-1962. https://collections.library.yale.edu/catalog/17049465.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 4, folder 145-146"])(1950-1962)[Creeley, Robert]. https://collections.library.yale.edu/catalog/17049465.