1:- module(func_issue_11, [count_unique/2]).    2:- use_module(library(func)).    3
    4count_unique(L,N) :-
    5    F = len of unique,
    6    N = F $ L.
    7
    8len(X,N) :-
    9    length(X,N).
   10
   11unique(XX,X) :-
   12    sort(XX,X)