father(a,e).
father(a,f).
father(c,g).
father(c,h).
father(e,i).
father(h,j).
father(h,k).
father(h,l).

mother(b,e).
mother(b,f).
mother(d,g).
mother(d,h).
mother(f,j).
mother(f,k).
mother(f,l).
mother(g,i).

male(a).
male(c).
male(e).
male(h).
male(i).
male(l).

female(b).
female(d).
female(f).
female(g).
female(j).
female(k).

brother(X,Y):-
    father(F,X),
    father(F,Y),
    X \= Y,
    male(X).

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

uncle(Uncle,Person) :-
    brother(Uncle,Parent),
    parent(Parent,Person). 

grand_parent(X,Y):-
    parent(X,Z),
    parent(Z,Y).

grand_father(X,Y):-
    father(X,Z),
    parent(Z,Y).