Robert Irwin, Part 1: Prologue: x18³, 1998. © Robert Irwin/Artists Rights Society (ARS), New York. Photo: Thibault Jeansen
Robert Smithson, Map of Broken Glass (Atlantis), 1969. Dia Art Foundation; Partial gift, Lannan Foundation, 2013. © Holt/Smithson Foundation/Licensed by VAGA at Artists Rights Society (ARS), NY. Photo: Florian Holzherr
Robert Whitman, Dante Drawings, 1974–75. © Robert Whitman. Photo: David Allison
Robert Ryman, Vector, 1975/1997. © Robert Ryman/Artists Rights Society (ARS), New York. Photo: Bill Jacobson Studio, New York. Image courtesy the Greenwich Collection, Ltd.