theorem
  for s being SortSymbol of S, x being Element of (the Sorts of A).s
  holds (x-term(A,V))@f = x
proof
  let s be SortSymbol of S, x be Element of (the Sorts of A).s;
  x = (root-tree x).{} by TREES_4:3;
  hence thesis by Th31,Th39;
end;
