At the 1934 EMS Colloquium

At the 1938 EMS Colloquium

At the 1951 EMS Colloquium

At the 1955 EMS Colloquium

At the 1959 EMS Colloquium

At the 1964 EMS Colloquium

At the 1968 EMS Colloquium

At the 1972 EMS Colloquium

At the 1976 EMS Colloquium