
theorem
  Borel_Sets c= L-Field
proof
  now let A be set;
    assume A1: A in Borel_Sets;
    set B = A;
    A = B \/ {};
    hence A in COM(Borel_Sets,B-Meas) by A1,Th75,MEASURE3:def 3;
  end;
  hence thesis;
end;
