 Also in 1957 he was appointed as a professor in the Institute of Statistics of the University of Paris.Théorie des graphes et ses applications Ⓣ was published in 1958 and, remarkably, in the following year his third book Espaces topologiques, fonctions multivoques Ⓣ was published.For a mathematician in their early thirties to publish three major books within as many years is a truly outstanding achievement.