theorem Th11:
  ex a being Element of R st x = Class(EqRel(R,I),a)
proof
  the carrier of R/I = Class EqRel(R,I) by Def6;
  then x in Class EqRel(R,I);
  then ex a being object
   st a in the carrier of R & x = Class(EqRel(R,I),a) by
EQREL_1:def 3;
  hence thesis;
end;
