Columbia subject headings:
Harvard subject headings:
Mathematicians--Italy--Correspondence.
Mathematicians--Sweden--Correspondence.
Mathematics--History--19th century
Mathematics--History--20th century
Mittag-Leffler, Magnus Gustaf, 1846-1927--Correspondence.
Volterra, Vito, 1860-1940--Correspondence.
Princeton subject headings:
Mathematicians--Italy--Correspondence.
Mathematicians--Sweden--Correspondence.
Mittag-Leffler, Magnus Gustaf, 1846-1927.
Personal correspondence.
Volterra, Vito, 1860-1940.