
theorem Th5:
  Sum(<*> ExtREAL) = 0.
proof
  reconsider F = <*> ExtREAL as FinSequence of ExtREAL;
  ex f being sequence of  ExtREAL st Sum F = f.(len F) & f.0 = 0. &
  for i being Nat st i < len F holds f.(i+1) = f.i+F.(i+1) by Def2;
  hence thesis;
end;
