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prologprolog-setof

the first query and duplicating elements in a list in Prolog

I am new to Prolog. I wrote the basic code below.

flight(acompany, paris, 7).
flight(bcompany,paris,7).
flight(ccompany,paris,7).
flight(dcompany,paris,7).

search([X],Y,Z) :- flight(X,Y,Z).

search([X|T],Y,Z) :- search(T,Y,Z) , flight(X,Y,Z).

I want to do two things. First when I query as 

?- search(X, paris,7).

the first thing prolog show me is 

X = [acompany]

But I want to see all element in the list at the first query.

i.e

X = [acompany, bcompany, ccompany, dcompany]

And the second thing I want is avoiding duplicating the elements in the list.

For example;

X = [acompany] ;
X = [bcompany] ;
X = [ccompany] ;
X = [dcompany] ;
X = [acompany, acompany] ;

I don't want such a last list.

How can I fix these two things? Thanks.

Solution 
  • ?- setof(X, flight(X, _, _), Xs).
Xs = [acompany, bcompany, ccompany, dcompany].