8.  Acknowledgements

      The authors are grateful for the thoughtful comments on how to organize this document from R. B. Brandt, E. N. Pinson and B. A. Tague. D. M. Ritchie made the system changes necessary to accommodate tracing within ADB. He also participated in discussions during the writing of ADB. His earlier work with DB and CDB led to many of the features found in ADB.