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+# Folder structure design
+
+## Concepts
+When we are optimizing solutions, we have the following strategies.
+- `draft`: create a new solution
+- `idea`: propose an idea to improve solutions
+- `merge`: merge different solutions
+
+
+Optimization is a long journey; we may switch between different strategies. These strategies are called routers.
+- `router`: a meta strategy to route between different strategies.  Router may have different implementations.
+
+
+Tools:
+- `select`: It provides features to be used by other strategies or steps.
+  1) `submit`: before we end the optimization, we have to select the only one solution to submit.
+  2) `expand`: we may have select one point to start the next expansion.
+
+
+## Suggest folder structure
+So the suggested folder structure is:
+```
+- router/
+- idea/
+  - samll_step(or refine?).py
+  - normal.py
+- draft/
+- merge/
+- select/
+  - expand.py
+  - submit.py
+```