Here is some old time systems theory from my Swedish summer reading.

Stafford Beer on Ross Ashby‘s Law of Requisite Variety in his paper “The Viable System Model: Its Provenance, Development, Methodology and Pathology” in The Journal of the Operational Research Society, Vol. 35, No. 1 (Jan., 1984), pp. 7-25

It has always seemed to me that Ashby’s Law stands to management science as Newton’s Laws stand to physics; it is central to a coherent account of complexity control. “Only variety can destroy variety.” People have found it tautologous; but all mathematics is either tautologous or wrong. People have found it truistic; in that case, why do managers constantly act as if it were false? Monetary controls do not have requisite variety to regulate the economy. The Finance Act does not have requisite variety to regulate tax evasion. Police procedures do not have requisite variety to suppress crime. And so on. All these regulators could be redesigned according to cybernetic principles…

Much more on Beer and Ashby can be found in Andrew Pickering’s fine book – the Cybernetic Brain – sketches of another future.