const n=12.

\begin{verbatim}

const b=5.

num(1..n).

box(1..b).


not_in(X,B) :- num(X),
                box(B),
                box(BB),
                not eq(B, BB),
                in(X,BB).

in(X,B)     :-  num(X),
                box(B),
                not not_in(X,B).

    :-  num(X),
        box(B),
        in(X,B),
        in(X+X, B).

    :-  num(X),
        num(Y),
        box(B),
        in(X,B),
        in(Y,B),
        in(X+Y, B).


hide not_in(X,Y).
hide num(X).
hide box(Y).

\end{verbatim}