Reputation: 1090
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.
This is not homework. This is a example problem for my exam. Thank you.
Upvotes: 0
Views: 2707
Reputation: 71065
Write it down:
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).
Now,
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.
Prolog lists are heterogeneous. An element might be a list as well. And its element too.
Upvotes: 1