Comments, with reply, on ´Using function abstraction to understand program behavior´ by P.A. Hausler et al

The commenter shows that an example given in the above-titled article (see ibid., vol.7, no.1, p.55-63 (1990)), namely a program for swapping the values of two variables, is incorrect, even though its correctness is proved by the author. Three of the authors respond, agreeing that the commenter´s point is valid and explaining the discrepancy.<>