误区链/ 2？

Question

如果我有（加载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

这给出了我期望的一个答案，但是：

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

我不希望答案如下：

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)]

带有as的条款在带有bs的条款之后。我有什么误会？

Answer 1

我现在可以看到我做错了什么。

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)]

显然在前两个元素的第三个参数中有1和2，因此满足链约束。