father(john,jane).

mother(jane,sue).

mother(jane,liz).

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

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

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

sibling(X,Y) :-
	parent(Z,X),
	parent(Z,Y),
	X \= Y.

mylength([],0).
mylength([_|T],N) :-
	mylength(T,LR),
	N is LR + 1.

member(_,[]) :- fail.
member(E,[E|_]).
member(E,[_|T]) :-
	member(E,T).

append([],L2,L2).
append([H|T],L2,[H|NL]) :-
	append(T,L2,NL).

factorial(0,1).
factorial(N,X) :-
	N > 0,
	Temp is N - 1,
	factorial(Temp, Y),
	!,
	X is N * Y.