Curator and historian, gallerist and writer: Klaus Kertess has long been a decisive and forward-thinking presence in the art world. He founded the Bykert Gallery in 1966, where he represented artists including Chuck Close, Ralph Humphrey, Brice Marden and Dorothea Rockburne; three decades later, he curated the 1995 Whitney Biennial, the follow-up to the famously political 1993 iteration. "What is being proposed here," he wrote in a catalogue essay...