theorem
  for D being non empty set, f being circular non empty FinSequence of D
  holds Rev f is circular
proof
  let D be non empty set, f be circular non empty FinSequence of D;
  thus (Rev f)/.1 = f/.len f by FINSEQ_5:65
    .= f/.1 by Def1A
    .= (Rev f)/.len f by FINSEQ_5:65
    .= (Rev f)/.len Rev f by FINSEQ_5:def 3;
end;
