Solution (source code)

= Solution

Put $u=\ln x$, so $du=dx/x$. The <integral> becomes $\int du/u$, giving
$$
\boxed{\int\frac{dx}{x\ln x}=\ln|\ln x|+C.}
$$
For the real <logarithm>, choose an interval in $0<x<1$ or $x>1$; the original <integrand> is singular at one and undefined for nonpositive $x$.