reserve X for non empty set,
  S for SigmaField of X,
  M for sigma_Measure of S,
  f,g for PartFunc of X,ExtREAL,
  E for Element of S;

theorem Th9:
  for x be Element of ExtREAL holds x|^1 = x
proof
  let x be Element of ExtREAL;
  Product(1 |-> x) = Product(<*x*>) by FINSEQ_2:59;
  hence thesis by Th7;
end;
