Robert Irwin. Interior/Exterior Window/Picture Planes Project Proposal Leo Castelli Gallery/Downtown, 1977. Pen and ink, transfer type, and graphite pencil on paper, Sheet: 24 × 27 5/8in. (61 × 70.2 cm). Whitney Museum of American Art, New York; gift of the artist, 77.46. ©Robert Irwen/Artists Rights Society (ARS), New York (Photo: Whitney Museum of American Art)