Prolog - necesito urgente

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Definir la relación suma_parcial(L1,X,L2) de forma que
% la lista L2 sea un subconjunto ordenado de L1 tal que la suma de sus
% elementos sea X.
%
% Ejemplos
%
% ?- suma_parcial([1,2,5,3,2],5,L).
% L = [1, 2, 2] ;
% L = [2, 3] ;
% L = [5] ;
% L = [3, 2] ;
% No
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% Autor:
% Fecha: 13/03/2008

borra(X, [X|L], L).
borra(X, [Y|L], [Y|L1]) :- borra(X, L, L1).