Shouldn't these two examples hold true?

[jgarte]

?- list_to_set([2,3,4,4,1,2], [2,3,4,1]).
%@    true.

Hi, shouldn't this return True or am I overlooking some constraint or detail? 🦆

?- list_to_set([2,3,4,4,1,2], [1,3,4,2]).
%@    false.

[triska]

One small note on terminology: "return" is terminology from functional programming; a predicate is true or holds.

list_to_set(Xs, Ys) relates the list Xs to a list Ys where each element of Xs occurs exactly once, and the first occurrences of each element are in the same order in both lists.

Therefore, we indeed expect the predicate to hold in the first example, but not in the second one.

[jgarte]

I've updated the title of this discussion to use the proper terminology. Thanks for the correction.

[jgarte]

and the first occurrences of each element are in the same order in both lists.

I missed this conjunction regarding list_to_set 🦆

Thanks for clarifying that for me. Much appreciated!

[jgarte]

The scryer-prolog documentation for list_to_set states the following:

Takes a list Ls0 and returns a list Set that doesn't contain any repeated element

https://www.scryer.pl/lists.html#list_to_set/2

I guess the conjunction part that you refer to is much more precise or clear in the Prolog ISO standard documentation? I don't have access to the ISO standard... 🦆

[UWN]

What is a function in functional programming often becomes a relation with functional dependencies in Prolog.

[jgarte]

Thanks for the additional context. Much appreciated.