theorem
  for s being SortSymbol of S, v being Element of V.s holds (v-term A)@f
  = f.s.v
proof
  let s be SortSymbol of S, v be Element of V.s;
  f.s.v = (root-tree f.s.v).{} by TREES_4:3;
  hence thesis by Th32,Th39;
end;
