reserve i,j,k,n for Nat;
reserve D for non empty set,
  p for Element of D,
  f,g for FinSequence of D;

theorem
  for x being object holds Rev <*x*> = <*x*>
proof
  let x be object;
  set f = <*x*>;
A1: len f = 1 by FINSEQ_1:39;
  now
    let i;
    assume i in dom f;
    then i in Seg len f by FINSEQ_1:def 3;
    then i = 1 by A1,FINSEQ_1:2,TARSKI:def 1;
    hence f.i = f.(len f - i + 1) by FINSEQ_1:39;
  end;
  hence thesis by Def3;
end;
