MLA

Purdy, James, 1914-2009. Frazier, Forrest. Box 2, folder 37. 1961-71, n.d.. https://collections.library.yale.edu/catalog/32210492.

APA, 6th edition

Purdy, James, 1914-2009. (["Box 2, folder 37"])(1961-71, n.d.)[Frazier, Forrest]. https://collections.library.yale.edu/catalog/32210492.