4 Aug 1998 / contributed to: ``From Newton to Einstein (A Festschrift in Honour of the 70th Birthday of Hans-Juergen Treder)'', W. Schroeder Editor, Bremen, Science Edition, 1998
16 May 2004 / IADIS International Conference on Applied Computing, Portugal, IADIS Press, Pedro Isaias et al. (Eds.), ISBN: 9729894736, Volume 2, pp. 39-42, 2004