列表列表的序言成员 [英] Prolog member of List of List

问题描述

我想定义一个谓词p(X)，其中X是列表的列表. p(X)是真的，如果X中只有一个元素Y，则X和Y没有公共元素.

I want to define a predicat p(X), where X is list of lists. p(X) is true, if in X there is only one element Y, that X and Y have no common elements.

这不是家庭作业.这是我考试的一个示例问题.谢谢.

This is not homework. This is a example problem for my exam. Thank you.

推荐答案

写下来:

p(X):-    %//  "define a predicate p(X), where X is list of lists, such that 
          %//   p(X) is true if in X there is only one element Y, 

  % findall( Y, (member(Y,X), ........ ), [_])

          %//   such that X and Y have no common elements".

    findall( Y, (member(Y,X), \+ have_common_element(X,Y) ), [_]).

have_common_element(A,B):- member(X,A), memberchk(X,B).

现在

8 ?- p([[1,[2]],[2],[3]]). %// both [2] and [3] have no common elts w/ X
false.

9 ?- p([[1,[2]],[2]]).     %// [1,[2]] has one common elt w/ X, viz. [2]
true.

序言列表是异构的.元素也可以是列表.还有它的元素.

Prolog lists are heterogeneous. An element might be a list as well. And its element too.

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