The rise of the mega-dealers, plus artists take over the Guggenheim

We talk to Michael Shnayerson about his book Boom, following the big art dealers from the 1940s to now. Plus, we speak to Nancy Spector, the organiser of Guggenheim in New York’s Artistic Licence: Six Takes on the Guggenheim Collection, and Paul Chan, one of the six artist-curators invited to mine the museum’s collection.