Sol LeWitt

Sol Lewitt's wall drawings at the Lisson Gallery, London, 2006. The drawings were originally shown at the same gallery in 1973. Photograph: Graeme Robertson/Guardian

Sol Lewitt's wall drawings at the Lisson Gallery, London, 2006. The drawings were originally shown at the same gallery in 1973. Photograph: Graeme Robertson/Guardian

Sol Lewitt's wall drawings at the Lisson Gallery, London, 2006. The drawings were originally shown at the same gallery in 1973. Photograph: Graeme Robertson/Guardian

A mural by artist Sol LeWitt in the entrance of Christie's auction house, New York. Photograph: Lynsey Addario/AP

Splotch #3, one of five sculptures and a wall drawing by Sol LeWitt, seen against the Manhattan skyline from the Iris and B Gerald Cantor roof garden of the Metropolitan Museum of Art, in New York, in 2005. Photograph: Richard Drew/AP

Splotch #15 (foreground), one of five sculptures and a wall drawing by Sol LeWitt displayed in the Iris and B Gerald Cantor roof garden of the Metropolitan Museum of Art, in New York, in 2005. Photograph: Richard Drew/AP

Artist Sol LeWitt in 2000. Photograph: Luciano del Castillo/EPA