reserve x, y, z for object,
  i, j, n for Nat,
  p, q, r for FinSequence,
  v for FinSequence of NAT;

theorem
  root-tree x = {[{},x]}
proof
  thus root-tree x = [:{{}},{x}:] by FUNCOP_1:def 2,TREES_1:29
    .= {[{},x]} by ZFMISC_1:29;
end;
