how to launch a subset query? #165

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1. EvgSkv commented on Sep 3, 2021

   

   EvgSkv

   on Sep 3, 2021

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   Hello!

   We need to check membership in the second list for each element in the first list.
   Here is the implementation and a test:

   @Engine("sqlite");
   
   # Returns 1 if a is subset of b and 0 otherwise.
   # To call as a predicate call Constraint(Subset(a, b)). 
   Subset(a, b) = result :-
     result_or_null Min= (e in b :- e in a),
     result == Coalesce(result_or_null, 1);
   
   # Testing Subset function.
   Test(a, b, Subset(a, b)) :-
     (a == [], b == [1,2]) |
     (a == [1,2], b == [1,2,3]) |
     (a == [1,2,3], b == [1,2]);
   

   Let me know if you have further questions.

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