reserve Omega for non empty set;
reserve Sigma for SigmaField of Omega;
reserve S for non empty Subset of REAL;
reserve r for Real;
reserve T for Nat;
reserve I for TheEvent of r;

theorem Th71:
  for a being Real holds {a} is Element of Ext_Borel_Sets
proof
  let a be Real;
  [.a,a.] is Element of Ext_Borel_Sets by Th70;
  hence thesis by XXREAL_1:17;
end;
