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

theorem Th5:
  for T being DecoratedTree st dom T = elementary_tree 0 holds
  T = root-tree (T.{}) by TARSKI:def 1,TREES_1:29;
