 This was one of his first papers on graph theory, his earlier work being on the theory of games and combinatorics.He was writing his famous book Théorie des graphes et ses applications Ⓣ at this time and had just published his book on the theory of games Théorie générale des jeux à n personnes Ⓣ (1957).Returning to France from the United States, Berge took up the position on Director of research at the Centre national de la recherche scientifique.