\begin{verbatim}

%ordering

 const length = 15.

 number(1..length).

 p(X) :- number(Y), X = Y * Y.

 between(X,Y)   :-  p(X),
                    p(Y),
                    p(Z),
                    X < Z,
                    Z < Y.

  next(X,Y)  :-  p(X),
                p(Y),
                X < Y,
                not between(X,Y).


 ord_p(N+1,X)   :-  p(X),
                p(Y),
                number(N),
                ord_p(N,Y),
                next(Y,X).


 not_ord_p(1,X) :- p(X),
                p(Y),
                Y < X.

 ord_p(1,X)     :-  p(X),
                not not_ord_p(1,X).

 hide number(X).
 hide not_ord_p(X,Y).
 hide next(X,Y).
 hide between(X,Y).
 hide p(X).

\end{verbatim}