Pettorossi, Alberto and Proietti, Maurizio and Senni, Valerio  The Transformational Approach to Program Development.   In:  A 25-Year Perspective on Logic Programming: Achievements of the Italian Association for Logic Programming, GULP.   Lecture Notes in Computer Science  (6125).  Springer, pp. 112-135.  ISBN 978-3-642-14308-3      (2010)