Columbia subject headings:
Luhmann, Niklas, 1927-1998.
Social systems.
Harvard subject headings:
Luhmann, Niklas, 1927-1998--Congresses.
Luhmann, Niklas--Criticism and interpretation.
Social systems--Congresses
Social systems.
System theory--Congresses
Princeton subject headings:
Luhmann, Niklas, 1927-1998.
Social systems.