Purdy letters
MLA
Stadler, Matthew, 1959-. Purdy letters. Box 5. 1977 2011. https://collections.library.yale.edu/catalog/16625109.
APA, 6th edition
Stadler, Matthew, 1959-. (["Box 5"])(1977 2011)[Purdy letters]. https://collections.library.yale.edu/catalog/16625109.