@ARTICLE {2559,
author={P.-Y. Schobbens and G. Saake and A. Sernadas and C. Sernadas},
doi={},
journal={Information Processing Letters},
title={U2: A two-level temporal logic for evolving specifications},
year={2002},
month={January},
volume={83},
number={3},
pages={167-172},
ISSN={0020-0190}
}