Leiris was a school-mate. Jacob, Apollinaire and especially Delaunay were good friends: meeting Jacob led him to Apollinaire, and then Picasso and Braque. Léger, Delaunay, Gleizes and he presented the first organised show of overtly cubist work. He joined Gris (met through Duchamp and Villon’s Puteaux group) and Lipchitz to avoid Paris bombardments towards the end of WWI; Rivera, Cendrars and Reverdy were among a circle of friends following the war. Popova was one of his students, and Gleizes his co-author on the first major study of cubism.