Louis Nirenberg and John Nash in Oslo, where they received the 2015 Abel Prize on May 19. Honored jointly “for striking and seminal contributions to the theory of nonlinear partial differential equations and its applications to geometric analysis,” they did not work together but, in the words of the Norwegian Academy, “influenced each other through their contributions and interactions.” A discussion of their main individual contributions appeared in the May issue of SIAM News. In a sad conclusion to a troubled life, Nash was killed with his wife when the taxi in which they were returning to their home in Princeton from the airport was involved in a collision. Nash had received the Nobel Prize in economics in 1994 for his early work in game theory.