proper support for "isabelle update -D DIR": avoid accidental exclusion of select_dirs (amending e5dafe9e120f);
@article{nowak2000,
title={Some elementary proofs of {P}uiseux’s theorems},
author={Nowak, Krzysztof Jan},
journal={Univ. Iagel. Acta Math},
volume={38},
pages={279--282},
year={2000}
}