Forde, G., Blumenfeld, E., & Citroen, P. R. (1993). Paul Citroen & Erwin Blumenfeld, 1919-1939: By Gerard Forde. Photographers' Gallery.
Cita Chicago (17th ed.)Forde, Gerard, Erwin Blumenfeld, i Paul Roelof Citroen. Paul Citroen & Erwin Blumenfeld, 1919-1939: By Gerard Forde. London: Photographers' Gallery, 1993.
Cita MLA (8th ed.)Forde, Gerard, et al. Paul Citroen & Erwin Blumenfeld, 1919-1939: By Gerard Forde. Photographers' Gallery, 1993.
Atenció: Aquestes cites poden no estar 100% correctes.