father(frank, jane).
father(james, anne).
father(john, frank).
father(james, sarah).
father(frank, tim).
mother(anne, jane).
mother(betty, frank).
mother(anne, tim).

parent(P, C) :- father(P, C).
parent(P, C) :- mother(P, C).

parents(C, M, F) :- 
  mother(M,C),
  father(F,C).

grandparent(G, C) :-
  parent(G, P),
  parent(P, C).

sibling(A, B) :-
  parent(P, A),
  parent(P, B),
  A \== B.

full_sibling(A, B) :-
  father(F, A),
  father(F, B),
  mother(M, A),
  mother(M, B),
  A \== B.
  
orphan(C) :- \+ parent(_, C).