Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!pyramid!nsc!taux01!shahaf
From: shahaf@taux01.UUCP (Shahaf Moshe)
Newsgroups: comp.lang.prolog
Subject: mine embarrassingly simple problem
Message-ID: <500@taux01.UUCP>
Date: 10 Mar 88 11:15:07 GMT
Reply-To: shahaf%taux01@nsc.UUCP (Shahaf Moshe)
Organization: National Semiconductor (Israel) Ltd.
Lines: 43

Hello, 
Can someone help me in the following: In translation from WATERLOO 
to Quintus code I need a !/1 predicate which does :
	      !(P) -  A  search through the
              ancestors exactly as for ancestor  and retry.   If this
              search fails then  the predicate fails.  If  the search
              succeeds then certain available  choices are eliminated
              from  an existing  portion of  the  proof.  All  choice
              points are  removed in the part  of the proof  from the
              point of selection of the given ancestor literal to the
              current point  in the proof.  Thus  a call of  the form
              /(*)  has exactly the same effect as the simple nullary
              / call. Consider the following example:
                   a:-b,c,d.
                   b:-e.
                   c:-f,g.
                   e.
                   f.
                   g:-/(c),h.
                   :-a.
                   ...
             The implication  tree has the  following form  when the
              unary cut is called:
 
                                  goal
                                   |
                                   a
                                 / | \
                                /  |  \
                               /   |   \
                              b    c    d
                             /     | \
                            /      |  \
                           e       f   g
                           x       x   | \
                                       |  \
                                     /(c)  h
             All choice points  from the selection of  c:-f,g onward
              are eliminated.  Thus if h fails an alternate proof for
              e will  be attempted  (and the  subproof of  c will  be
              deleted).

thanks a lot.

shahaf%taux01@nsc.COM