reserve a,b,i,j,k,l,m,n for Nat;

theorem RFP:
  for f be FinSequence holds
    Rev (idseq (len f)) is Permutation of dom (Rev f)
  proof
    let f be FinSequence;
    dom (Rev f) = dom f by FINSEQ_5:57
    .= Seg(len f) by FINSEQ_1:def 3;
    hence thesis by MATRIX94;
  end;
