
prune_instances(+List, -PrunedList)

   Succeeds if PrunedList is the smallest list that subsumes the list List.



Arguments
   List                List of instantiated terms.
   PrunedList          List or variable.

Type
   Comparing and Sorting

Description
   Used to get the smallest list PrunedList whose elements subsume elements
   of the list List.  List must not contain variables.  If List contains
   elements which are variants of each other, then of these, PrunedList
   will only contain the first element found.  If List contains element(s)
   which are instances of another element, then of these, PrunedList will
   only contain the latter.


   Note that if List contains only ground terms, it cannot contain proper
   instances or variants, but only duplicates.  Therefore, it is faster to
   use a sorting predicate to prune it.




Modes and Determinism
   prune_instances(+, -) is det

Examples
   
Success:
      prune_instances([5,2,3,5,4,2],L).
          (gives L=[5,2,3,4]).

      prune_instances([f(1,2),f(1,M),1],L).    % instance
          (gives L=[f(1,M),1]).

      prune_instances([f(1,2,3),f(1,M,3),f(1,2,N)],L).
          (gives L=[f(1,M,3),f(1,2,N)]).

      prune_instances([f(1,N),f(1,M),1],L).    % variants (first one retained)
          (gives L=[f(1,N),1]).

      prune_instances([f(1,X),f(1,2),g(1)],L).
          (gives L=[f(1,X),g(1)]).

      :- lib(ic).
      X::2..5, prune_instances([1,3,X,5,8], L).
          (gives L=[X,1,8]).
Fail:
      prune_instances([1,2,3,1,4,2],[2,3,4]).





See Also
   sort / 2, sort / 4
