Lambrecht, L. (1998). Günter Umberg met Bernard Frize, Olivier Mosset, Jo Baer, Fabian Marcaccio, Marte Wéry, David Reed, Helmut Federle, Carl Ostendarp, Elisabeth Vary, Mary Heilmann, Keith Sonnier, Robert Zandvliet mer Vaste collectie Museum Dhondt-Dhaenens.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रLambrecht, Luk. Günter Umberg Met Bernard Frize, Olivier Mosset, Jo Baer, Fabian Marcaccio, Marte Wéry, David Reed, Helmut Federle, Carl Ostendarp, Elisabeth Vary, Mary Heilmann, Keith Sonnier, Robert Zandvliet Mer Vaste Collectie Museum Dhondt-Dhaenens. Deurle, 1998.
एमएलए (8वां संस्करण) प्रशस्ति पत्रLambrecht, Luk. Günter Umberg Met Bernard Frize, Olivier Mosset, Jo Baer, Fabian Marcaccio, Marte Wéry, David Reed, Helmut Federle, Carl Ostendarp, Elisabeth Vary, Mary Heilmann, Keith Sonnier, Robert Zandvliet Mer Vaste Collectie Museum Dhondt-Dhaenens. 1998.