reserve n, k, r, m, i, j for Nat;

theorem
  Seq (FIB| {2}) = <*1*>
proof
  reconsider H = {[2,FIB.2]} as Function;
A1: dom H = {2} by RELAT_1:9;
  dom H c= Seg 2
  proof
    let x be object;
    assume x in dom H;
    then x = 2 by A1,TARSKI:def 1;
    hence thesis;
   end;
  then reconsider H as FinSubsequence by FINSEQ_1:def 12;
  2 in NAT;
  then 2 in dom FIB by FUNCT_2:def 1;
  then Seq (FIB | {2}) = Seq H by GRFUNC_1:28
    .= <*FIB.2*> by FINSEQ_3:157
    .= <*1*> by Def2,Th21;
  hence thesis;
end;
