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https://gpt-index.readthedocs.io/en/stable/examples/agent/openai_agent_context_retrieval.html#use-uber-10-q-as-context-use-calculator-as-tool
I am using ContextRetrieverOpenAIAgent from this example, I want to get context injection from different chunks of data from my index. The first example uses query engine tools and 2nd one uses retriever for this. How do they differ and which one should I use, thank you.