How is the query working without an llm specified?

Hi all,

I’m currently going through the “LangChain for LLM Application Development” course and even though I’m understanding most of it and am starting to play with the library there’s one thing that I cannot understand at all.

In the 5th part / video of this course between 2:30 and 3:30 approximately (or between the 8th and 11th cell), the course shows the quickest way to do a quick QA over a document.
However at that point in the code, no llm has ever been called or invoked and when I look at the documentation of the methods/classed used I don’t see any “default llm” or such in cas none is given.

So how is the response generated if no llm is called ?

Thanks a lot for your help this is really mysterious for me