Problem2　偶数のフィボナッチ数

問題

% problem 2
solve:-
	fibo([2,1],Fibo),
	even_sum(Fibo,Sum),
	write(Sum).
	
even_sum([],0):-!.
even_sum([First|Rest],Sum):-
	First mod 2 =:= 0,
	!,
	even_sum(Rest,Sum1),
	Sum is First + Sum1.
even_sum([_|Rest],Sum):-
	even_sum(Rest,Sum).
	
	
fibo([First|Rest],Rest):-
	First >= 4000000,
	!.
fibo([P1,P2|Rest],Out):-
	P0 is P1 + P2,
	fibo([P0,P1,P2|Rest],Out).

実行結果：
1 ?- solve.
***********************(解答伏せます)**********************
true.