# Khintchine theorem - necessity of monotonicity in divergence condition

Hi,

I'm trying to get a hold of Khintchine theorem in metric Diophantine approximation. Right now I'm interested in the divergence condition, namely:

If $\sum_{q=1}^\infty\psi(q) = \infty >$ and $\psi$ monotonically decreasing then $\lambda(\phi-approx)^c)=0$ (when $\psi(q) = q\phi(q)$, and $\phi-approx$ is the set of all $\theta$ such that there is an infinite number of solutions to $\|\theta - \frac{p}{q}\| < \phi(q)$).

I'm having trouble finding an example for the necessity of the monotonicity condition (=given a function that is not, $\lambda(\phi-approx)=0$). After some searching, I've found it mentioned in an article "Khintchine’s problem in metric Diophantine approximation" by R. J. Duffin, A. C. Schaeffer. Unfortunately I don't have access to it (and neither my university library). Maybe someone has a free access link to it or could explain it shortly?