theorem Th88:
  for x ex t st x = LD-EqClassOf t
proof
  let x;
  x in Class LD-EqR;
  then consider a such that
  A1: a in GRZ-formula-set and
  A2: x = Class(LD-EqR, a) by EQREL_1:def 3;
  reconsider t = a as GRZ-formula by A1;
  take t;
  thus thesis by A2;
end;
