MLA

Wheeler, Monroe, 1899-1988. Mondrian, Piet. Box 7, folder 208. 1942 Mar 5. https://collections.library.yale.edu/catalog/33496098.

APA, 6th edition

Wheeler, Monroe, 1899-1988. (["Box 7, folder 208"])(1942 Mar 5)[Mondrian, Piet]. https://collections.library.yale.edu/catalog/33496098.