Trials and Tribulations of Collaboration: Pablo Léon de la Barra sends us a long letter from Tripoli and Jon Leon writes about the fashionable rise of the visor. Pablo Larios portrays the Berlin-based artist Simon Denny. Bruce Hainley talks to painter Brian Calvin about his collaboration with Raf Simons. We visit the gallery project “curated by” in Vienna, and the artist collective Am Nuden Da in London.