theorem Th15:
  for p being Tuple of 1,REAL holds - p is Tuple of 1,REAL
  proof
    let p be Tuple of 1,REAL;
    consider d be Element of REAL such that
A1: p = <* d *> by FINSEQ_2:97;
    -p = <* -d *> by A1,RVSUM_1:20;
    hence thesis;
  end;
