theorem Th64:
  g <> 1_(H.i) implies nf [* i, g *] = <* [i,g] *>
proof
  assume g <> 1_(H.i);
  then A1: <* [i,g] *> is_a_normal_form_wrt ReductionRel H by Th38;
  [i,g] in FreeAtoms(H) by Th9;
  then <*[i,g]*> is FinSequence of FreeAtoms(H) by FINSEQ_1:74;
  hence thesis by A1, Th48, Def7;
end;
