Columbia subject headings:
Beuys, Joseph--Exhibitions.
Mail art--Exhibitions.
Saint-Phalle, Niki de, 1930-2002--Exhibitions.
Harvard subject headings:
Artists--Correspondence--In art--Exhibitions.
Beuys, Joseph--Correspondence--Exhibitions.
Letters in art--Exhibitions.
Postcards in art--Exhibitions.
Saint-Phalle, Niki de, 1930-2002--Correspondence--Exhibitions.
Princeton subject headings: