误解链/ 2？

Question

如果我（装有clpfd）：

test1(Ps):-
    permutation(Ps,[(a,1,1),(b,2,2),(c,3,1),(d,4,2)]), 
    Ps =[(L1,W1,X1),(L2,W2,X2),(L3,W3,Y1),(L4,W4,Y2)], 
    chain([W1,W2,W3,W4],#<).

并查询：

?-test1(P).
P = [(a,1,1), (b,2,2), (c,3,1), (d,4,2)]
false

哪个给出了我期望的答案，但是带有：

test2(Ps):-
    permutation(Ps,[(a,1,1),(b,2,2),(c,3,1),(d,4,2)]), 
    Ps =[(L1,W1,X1),(L2,W2,X2),(L3,W3,Y1),(L4,W4,Y2)], 
    chain([X1,X2],#<).

查询：

?-test2(P):-
P = [(a,1,1), (b,2,2), (c,3,1), (d,4,2)]
P = [(a,1,1), (b,2,2), (d,4,2), (c,3,1)]
P = [(a,1,1), (d,4,2), (b,2,2), (c,3,1)]
P = [(a,1,1), (d,4,2), (c,3,1), (b,2,2)]
P = [(c,3,1), (b,2,2), (a,1,1), (d,4,2)]
P = [(c,3,1), (d,4,2), (a,1,1), (b,2,2)]
P = [(c,3,1), (b,2,2), (d,4,2), (a,1,1)]
P = [(c,3,1), (d,4,2), (b,2,2), (a,1,1)]
false

我不希望像这样的答案

P = [(c,3,1), (b,2,2), (d,4,2), (a,1,1)]
P = [(c,3,1), (d,4,2), (b,2,2), (a,1,1)]

其中带有as的术语位于带有bs的术语之后。 我有什么误会？

Answer 1

我现在可以看到我做错了。

作为答案：

P = [(c,3,1), (b,2,2), (d,4,2), (a,1,1)]
P = [(c,3,1), (d,4,2), (b,2,2), (a,1,1)]

在前两个元素的第三个参数中显然有1和2，因此满足链约束。