theorem Th108:
  for t being ground pure expression of C, a_Type C
  holds ({} QuasiAdjs C) ast t is ground
proof
  let t be ground pure expression of C, a_Type C;
  set T = ({} QuasiAdjs C) ast t;
  thus variables_in T = variables_in t by Th106
    .= {} by Th107;
end;
