MLA

Koch, Frederick R. (Frederick Robinson). Music/Ich möchte hingehn. Box 127, folder 1469. n.d.. https://collections.library.yale.edu/catalog/2029237.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 127, folder 1469"])(n.d.)[Music/Ich möchte hingehn]. https://collections.library.yale.edu/catalog/2029237.