

















   Purpose: Implement Mackworth's AC-3 algorithm.
%   Needs  : Util:Assoc.Pl, Ut
istUt.Pl

/*  It is often stated that blind backtracking is highly inefficie
and
    it is thereby implied that Prolog must be highly inefficient.  I
s
    article "Consistency in Networks of Relations" (AIJ 8 (1977) 9
8)
  
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