Check if all tuples in a list are different (ECLiPSe) <p>I have a list with tuples like this:</p> <pre><code>[(1,2),(5,3),(6,7)] </code></pre> <p>I'm trying to write a predicate that checks if all tuples in a list are different. The following line works for a list with integers but not for a list with tuples:</p> <pre><code>all_diff(L) :- \+ (select(X,L,R),member(X,R)). </code></pre> <p><code>member/2</code> works fine to check if a tuple is in a list but it is the <code>select/3</code> that has problems with tuples. It gives a type error.</p> <p>How do I check if all tuples are different?</p>