%% --------------------------------------
%% Some information about the Bush family. 
%% --------------------------------------

mother(barbara, georgejr).

father(georgejr, jenna).

father(georgejr, barbara2).

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

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

grandmother(X,Z) :- mother(X,Y), parent(Y,Z), 
      write('Solution = '), write(Z), nl, fail.

% -------------------------
% A definiton for factorial.
% -------------------------

factorial(0,1).

factorial(N,A) :-
  N > 0,
  N1 is N - 1,
  factorial(N1,B),
  A is N * B.

% ------------------------------------------------
% Counting the number of top level items in a list.
% ------------------------------------------------

count([],0).

count([A|B],N) :- count(B,X), N is 1 + X. 

% -----------------------
% A definition for append.
% -----------------------

myappend([], X, X).

myappend([X|Y], Z, [X|W]) :-
  myappend(Y,Z,W).