{"ast_node_type":"other","tokens":[{"end":52,"kind":"keyword","start":0,"text":"self.undo_log.push(AddCombination(t,"}]}
        self.undo_log.push(AddCombination(t, vars));
        self.combine_map(t).insert(vars, c);
        let new_r = ty::Region::new_var(tcx, c);