The docs for
list_to_ord_set/2 don’t tell you that it also removes duplicates. If that’s inherent to the definition of a set in SWI-Prolog then adding a note that indicates that might be considered redundant. But for someone coming to the page that doesn’t know that about SWI-Prolog sets it might be helpful. My two cents:
[trace] 58 ?- list_to_ord_set([c,d,a,c,d,e], X). X = [a, c, d, e].