def do_back(self, line):
        "Go back one step. From entity => ontology; from ontology => ontospy top level."
        if self.currentEntity:
            self.currentEntity = None
            self.prompt = _get_prompt(self.current['file'])
        else:
            self.current = None
            self.prompt = _get_prompt()
Go back one step. From entity => ontology; from ontology => ontospy top level.