reserve i,j for Element of NAT,
  x,y,z for FinSequence of COMPLEX,
  c for Element of COMPLEX,
  R,R1,R2 for Element of i-tuples_on COMPLEX;

theorem Th5:
  for x being complex-valued FinSequence holds len (-x)=len x
proof
  let x be complex-valued FinSequence;
  dom (-x)=dom x by VALUED_1:8;
  hence thesis by FINSEQ_3:29;
end;
