gistfile1.pro

male(terah). 
male(abraham).
male(nahor). 
male(haran).
male(isaac). 
male(ismael).
male(jacob).

female(sarah). 
female(hagar). 

father(terah, sarah). 
father(terah, abraham). 
father(abraham, isaac). 
father(isaac, jacob). 
father(abraham, ismael). 

mother(sarah,isaac).
mother(hagar,ismael).

parent(Parent,Child) :- father(Parent,Child).
parent(Parent,Child) :- mother(Parent,Child).

son_of(Child,Parent) :-
  male(Child), parent(Parent,Child).

daughter_of(Child,Parent) :-
  female(Child), parent(Parent,Child).

grandparent_of(GrandChild,GrandParent) :-
  distinct( (GrandParent,GrandChild),
            (parent(GrandParent,Someone),parent(Someone,GrandChild)) ).


ancestor_of(Descendant,Ancestor) :- 
  distinct( (Ancestor,Descendant),parent(Ancestor,Descendant)).
ancestor_of(Descendant,Ancestor) :-
  distinct((Ancestor,Descendant),
   (parent(Ancestor,X), ancestor_of(Descendant,X))).