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parent(harriet, george).
parent(george, richard).
parent(george, amelia).
parent(george, susan).
parent(matilda, richard).
parent(matilda, amelia).
parent(victoria, susan).
parent(richard, sophie).
parent(richard, joseph).
parent(ellen, sophie).
parent(ellen, joseph).
parent(susan, charles).
parent(walter, charles).

male(arthur).
male(george).
male(richard).
male(joseph).
male(walter).
male(charles).

female(harriet).
female(matilda).
female(victoria).
female(amelia).
female(susan).
female(ellen).
female(sophie).

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

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

father(X, Y) :- parent(X, Y), male(X).
mother(X, Y) :- parent(X, Y), female(X).
sibling(X, Y) :- parent(P, X), parent(P, Y), X \= Y.
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