As $x \rightarrow \infty$, we can write $(1+x)^{-1}$ as a geometric series:
$(1+x)^{-1} = 1 - x + x^2 - x^3 + \cdots$
Now, let's find the asymptotic expansion of the function $\left(1+e^{-x}\right)(1+x)^{-1}$ as $x \rightarrow \infty$.
We can rewrite the
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