[Postcard: 1939 February 20, Hampstead, Piet Mondrian to Mr. Carel Mondriaan, Breda, Holland]
MLA
Mondrian, Piet, 1872-1944, Tuck, Raphael, & Sons, ltd., publishers, London. . [Postcard: 1939 February 20, Hampstead, Piet Mondrian to Mr. Carel Mondriaan, Breda, Holland]. Box 1 | Folder 1. 1939 February 20. https://collections.library.yale.edu/catalog/10061356.
APA, 6th edition
Mondrian, Piet, 1872-1944, & Tuck, Raphael, & Sons, ltd., publishers, London. . (["Box 1 | Folder 1"])(1939 February 20)[[Postcard: 1939 February 20, Hampstead, Piet Mondrian to Mr. Carel Mondriaan, Breda, Holland]]. https://collections.library.yale.edu/catalog/10061356.