Equation 3 · Part 2 · Retrieval Is an Evidence System, Not a Memory
Symbol x
What this part means
the writing.
Its job in the formula
x is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
Full expression→Symbol x→Article meaning
Where the article explains it
Writing x for the query, y for the output, and for the top k passages returned by a retriever with parameters :
The passage around this formula
The retrieval literature said the opposite. Lewis and colleagues introduced RAG explicitly as a combination of parametric and non-parametric memory, and the architectural point is that the second is a different kind of object, not an extension of the first [ 1 ] . Their formulation treats the retrieved passage as a latent variable to be marginalised over. Writing x for the query, y for the output, and for the top k passages returned by a retriever with parameters :
Learn the underlying idea
A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.
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Sources cited in the surrounding passage
These citations provide research context; check each source for the exact claim it supports.