Meeting under the integral sign : the Oslo congress of mathematicians on the eve of the Second World War Introduction: Four strategies the prehistory of the Oslo Congress and sources The Norwegian hosts : the newcomer with historical traditions The German delegation : swaying between expansionism and isolationism The Russian withdrawal : isolationism out of fear and ideology The Italian case : mathematics as a victim of world politics The Congress in the Norwegian dailies International mathematics shortly before and after the Second World War : a glimpse ahead and back again Assessing the mathematics of the Congress The plenary lectures ICMI Conclusions regarding the mathematics of the Congress.