This paper
appears in ACM Quote Quad, Volume 26, Number 4, Pages 55-62,
June 1996. Copyright ©1996, ACM. Permission to copy without fee all or part of this
material is granted provided that the copies are not made or distributed for
direct commercial advantage, the ACM copyright notice and the title of
the publication and its date appear, and notice is given that copying
is by permission of the Association for Computing Machinery. To copy
otherwise, or to republish, requires a fee and/or specific permission.
The paper was presented at the APL 96 Conference at Lancaster University,
UK, July 29, 1996.
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