Re: how to refractor this ?

I made my gene to this :

male(roelof).
male(mans). 
male(ronald).
male(jan).

female(chantal).
female(marie).
female(gerda).
female(dagmar).
female(denise).
female(kimberly).

% parent (X,Y) means that X is a parent of Y. 
parent(mans,gerda).
parent(mans,roelof).
parent(marie,gerda).
parent(marie,roelof).
parent(dagmar,denise).
parent(dagmar,kimberly).
parent(ronald,denise).
parent(ronald,kimberly).
parent(chantal,tamara).
parent(roelof,tamara).
parent(jan,chantal).
parent(jan,dagmar).

% checks if a Child has a father. 
father_child(Father, Child) :-
 parent(Father, Child),
 male(Father).

%checks if a Child has a mother.
mother_child(Mother, Child) :-
 parent(Mother, Child),
 female(Mother).

%checks if two children (child, sibling) have the same father.
same_father(Child, Sibling) :-
 father_child(Father, Child),
 father_child(Father, Sibling).

%checks if two children (child, sibling) have the same mother.
same_mother(Child, Sibling) :-
 mother_child(Mother, Child),
 mother_child(Mother, Sibling).

%checks if a Child has a sibling. 
siblings(Child, Sibling) :-
       same_father(Child, Sibling),
       Child \== Sibling ;
       same_mother(Child, Sibling),
       \+ same_father(Child, Sibling).

%display the names of the siblings of a child. Works with one unknown and both unknown.
display_siblings(X,Y):-
     setof(X-Y, (siblings(X,Y), X @< Y), Sibs),
     write(Sibs).

%checks if a child has a brother. 
brother_child(Child, Brother) :- 
     siblings(Child, Brother), 
     male(Brother).


%displays the name of a brother of a child.
display_brother(X,Y) :-
      setof(X-Y, (brother_child(X,Y), X @< Y),Brother),
      write(Brother).

%checks if a child has a sister.
sister(Person, Sister) :- 
     siblings(Child, Sister), 
     female(Sister).

%displays the name of the sister of a child. Works with (x,y) and (child,X).
display_sisters(Person) :-
        write('% sisters of '), write(Person), nl,
        (   sister(Person, Sister),
            portray_clause(sister(Person, Sister)),
            fail
            ;   true
            ),
        write('% end'), nl.


but this does not work. 

When I do :

display_sister(X) I see this output:

?- display_sisters(X).
% sisters of _G817
sister(_, gerda).
sister(_, kimberly).
sister(_, denise).
sister(_, dagmar).
sister(_, chantal).
% end

So I miss the name of which person the second name is a sister.
And I see that for example  sister(_, kimberly) and (_,denise) this is a duplicate which I try to avoid. 

When I do this: 

display_sisters(gerda) I see this : 

?- display_sisters(gerda).
% sisters of gerda
sister(gerda, gerda).
sister(gerda, kimberly).
sister(gerda, denise).
sister(gerda, dagmar).
sister(gerda, chantal).

Which is not right. Gerda has no sisters. She is not a sister of her own. Kimberly. Denise and Dagmar are for certain 
no sisters. Dagmar is a sister of my wife and Kimberly and Denise are her children. 

Chantal is my wife. So she would be a sister-in-law. 

Roelof

 		 	   		  
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