MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Schwitters, Kurt. Box 113, folder 2707-2713. 1922-48, n.d.. https://collections.library.yale.edu/catalog/2015232.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 113, folder 2707-2713"])(1922-48, n.d.)[Schwitters, Kurt]. https://collections.library.yale.edu/catalog/2015232.