{"ast_node_type":"other","tokens":[{"end":40,"kind":"keyword","start":0,"text":"self.undo_log.push(AddVar(vid));"}]}
        self.undo_log.push(AddVar(vid));
        assert_eq!(vid, u_vid.vid);
        debug!("created new region variable {:?} in {:?} with origin {:?}", vid, universe, origin);