The Free On-line Dictionary of Computing (30 December 2018):

Set Equation Transformation System
SETS

    (SETS) A system for symbolic manipulation of Boolean
   equations.

   ["Efficient Ordering of Set Expressions for Symbolic
   Expansion", R.G. Worrell et al, J ACM 20(3):482-488, Jul
   1973].

   (2017-12-04)