reserve x,y,z for set;
reserve f,f1,f2,f3 for FinSequence,
  p,p1,p2,p3 for set,
  i,k for Nat;
reserve D for non empty set,
  p,p1,p2,p3 for Element of D,
  f,f1,f2 for FinSequence of D;

theorem
  f:-p:-p = f:-p
proof
A1: (<*p*>^(f/^p..f))/.1 = p by FINSEQ_5:15;
  thus f:-p:-p = (<*p*>^(f/^p..f)):-p by FINSEQ_5:def 2
    .= <*p*>^(f/^p..f) by A1,Th44
    .= f:-p by FINSEQ_5:def 2;
end;
