<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def adj_par_names(self):
 """ wrapper around pyemu.Pst.adj_par_names for list adjustable parameter names Returns ------- adj_par_names : list pyemu.Pst.adj_par_names """

        if self.__pst is not None:
            return self.pst.adj_par_names
        else:
            return self.jco.par_names