This is for:
Abramson, D.A. and Sosic, R. "Relative Debugging using Multiple Program Versions", Key Note Address, 8th Int. Symp. on Languages for Intensional Programming , Sydney, 3-5th May, 1995. In Intensional Programming I, World Scientific, ISBN 981-02-2400-1.
(From https://web.archive.org/web/19970504170226/https://www.cit.gu.edu.au/~davida/guard.html.)
Linked to archived paper: https://web.archive.org/web/19970504170226/https://www.cit.gu.edu.au/~davida/papers/islip.ps.Z