
theorem Th19:
  for p be complex-valued FinSequence for i be Nat st i < len p
  holds Sum (p|(i+1)) = Sum (p|i) + p.(i+1)
proof
  let p be complex-valued FinSequence;
  let i be Nat;
  assume i < len p;
  then p|(i+1) = p|i ^ <*p.(i+1)*> by FINSEQ_5:83;
  hence thesis by RVSUM_2:31;
end;
