🚀 go-pugleaf

In article <1992Dec13.173016.8849@nntp.hut.fi> jur@robin.cs.hut.fi (Jussi Rintanen) writes:

>   Question 1: What implementations of Prolog implement the occurs check?
>   (Our university has both Sicstus and NU-Prolog.)
>


Try SEPIA-Prolog  from  ECRC  in munich/Germany.  It   has   some nice
features, including the  possibility  for sound unification.  It  also
includes "iterative deepening", so you need not program it explicitly.
Sepia is cheap and pretty fast. Contact sepia_request@ecrc.de (i'm not
quite sure about this adress)

As an alternative you could "linearize" the heads of your rules, i.e.
eliminate multiple occurences of variables in the head. For example, 
your rule

	axiom(impl(A,impl(B,A)),k).

then becomes

	axiom(impl(A,impl(B,A1)),k) :- unify(A,A1).

where unify/2 is a sound unification procedure, as can be found e.g. 
in the quintus library. This works sufficiently well for many
programs. However, the first alternative, a Prolog with built-in sound
unification, is superior (wrt. efficiency).

	Peter
--
____________________________________________________________________
Peter Baumgartner                      | peter@infko.uni-koblenz.de
Universitaet Koblenz,                  |
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