reserve n,m for Nat;

theorem
  for f being real-valued FinSequence holds sort_d (-f) = - (sort_a f)
proof
  let f be real-valued FinSequence;
  -f,sort_d(-f) are_fiberwise_equipotent by Def5;
  then
A1: --f,-sort_d(-f) are_fiberwise_equipotent by Th25;
  -sort_d (-f) is non-decreasing by Th22;
  then -sort_d (-f)=sort_a f by A1,Def6;
  hence thesis;
end;
