reserve i,j,n,k for Nat,
  a for Element of COMPLEX,
  R1,R2 for Element of i-tuples_on COMPLEX;

theorem Th45:
  for F being FinSequence of COMPLEX holds len F = 1 implies Sum F = F.1
proof
  let F be FinSequence of COMPLEX;
  assume len F = 1;
  then F = <* F.1 *> by FINSEQ_1:40;
  hence thesis by FINSOP_1:11;
end;
