Sorts the elements of the list List1 into the ascending standard order, and removes any multiple occurrences of an element. The resulting sorted list is unified with the list List2.
| ?- sort([a,X,1,a(x),a,a(X)], L). L = [X,1,a,a(X),a(x)]
(The time taken to do this is at worst order (N log N) where N is the length of the list.)