1. summary generation (naive way, need to make it efficient) 2. parameter propagation (depends on which one to propagate) 3. fix a bug of smashing recursive fields 4. more checks in Checker 5. next steps: think about how to do instantiation (e.g. the order, how to do mapping from which level (node or location), how to post-merge efficiently, how to link pre-merge and post-merge)