Return the names of sections ordered by ordkey.
        For the time being, the values are taken from the first timer.

def section_names(self, ordkey="wall_time"):
        """
        Return the names of sections ordered by ordkey.
        For the time being, the values are taken from the first timer.
        """
        section_names = []

        # FIXME this is not trivial
        for idx, timer in enumerate(self.timers()):
            if idx == 0:
                section_names = [s.name for s in timer.order_sections(ordkey)]
                #check = section_names
                #else:
                #  new_set = set( [s.name for s in timer.order_sections(ordkey)])
                #  section_names.intersection_update(new_set)
                #  check = check.union(new_set)

        #if check != section_names:
        #  print("sections", section_names)
        #  print("check",check)

        return section_names