H. Von Foerster wikipedia 
, Understanding understanding: essays on cybernetics and cognition. New York: Springer, 2003.
Bibliothekare und Technik: eine Mesalliance? "Technology – What Will it Mean to Librarians?", Illinois Libraries vol. 53(9), 1971, 785-803.
YOUTUBE sWNw-h981x0 An interview (in German) with Fritz B. Simon about his memories of Heinz von Foerster
The book discussed in the preceding contributions [in: *Sinn, Kommunikation und soziale Differenzierung* (Meaning, Communication and Social Differentiation)] makes the proposal to sociology to adopt the concept of Autopoiesis and thus to gain a more profound theory of self-referential systems that also includes elementary operations.
On the death of Humberto R. Maturana (September 14, 1928 – May 6, 2021) by Dirk Baecker
Heinz von Foerster's concept of operational closure:
Yveline Rey: Interview with Heinz von Foerster
“Change” is not yet accompanied by an appropriate imperative. Let me remedy this situation at once by inventing an imperative for you; the therapeutic imperative: “If you want to be yourself, change!” Is this paradoxical? Of course! What else would you expect from change? -- Heinz von Foerster ⇒ The Ethical Imperative
The problem is “I,” the shortest selfreferential loop. When speaking about oneself, using “I,” magic is performed. One creates oneself by creating oneself. “I” is the Operator who is the result of the Operation. -- Heinz von Foerster ⇒ The Ethical Imperative