'Useful for usderstanding/debugging the algorithms.  Not
generally activated in end-user code.'

def db_trace(self, msg):

    if self.debug:
        letters = 'abcdefghijklmnopqrstuvwxyz'
        state = [self.f, self.lpart, self.pstack]
        print('DBG:', msg, [''.join(part) for part in list_visitor(state, letters)], animation_visitor(state))
