Query: What did Lok-Ham Chan claim  Changchub Gyaltsen wanted to remove?
Context: However, Lok-Ham Chan, a professor of history at the University of Washington, writes that Changchub Gyaltsen's aims were to recreate the old Tibetan Kingdom that existed during the Chinese Tang dynasty, to build "nationalist sentiment" amongst Tibetans, and to "remove all traces of Mongol suzerainty." Georges Dreyfus, a professor of religion at Williams College, writes that it was Changchub Gyaltsen who adopted the old administrative system of Songtsän Gampo (c. 605–649)—the first leader of the Tibetan Empire to establish Tibet as a strong power—by reinstating its legal code of punishments and administrative units.