theorem Th4:
  for s being SortSymbol of S, v being Element of V.s holds
  root-tree [v,s] is Term of S, V
proof
  let s be SortSymbol of S, v be Element of V.s;
  reconsider vs = [v,s] as Terminal of DTConMSA V by MSAFREE:7;
  root-tree vs in TS DTConMSA V;
  hence thesis;
end;
