gender(al,male).
gender(anne,female).
gender(arthur,male).
gender(amber,female).
gender(boris,male).
gender(barbara,female).
gender(betty,female).
gender(buck,male).
gender(carla,female).
gender(charles,male).
gender(cora,female).
gender(cuthbert,male).
gender(cecilia,female).
gender(calvin,male).

father(arthur,buck).
father(al,buck).
father(amber,buck).
father(anne,boris).
father(barbara,charles).
father(betty,cuthbert).
father(boris,charles).
father(buck,calvin).

mother(al,barbara).
mother(anne,betty).
mother(arthur,barbara).
mother(amber,barbara).
mother(boris,carla).
mother(barbara,carla).
mother(betty,cora).
mother(buck,cecilia).

parent(X,Y) :- father(X,Y).
parent(X,Y) :- mother(X,Y).

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