:- set_prolog_flag(verbose,silent).
:- prompt(_, '').
:- use_module(library(readutil)).
 
main:-
	process,
	halt.
 
skip(_,[],[]).
skip(X, [X|T], T).
skip(X, [Y|T], [Y|T]) :- X \= Y.
 
remove_dups([], []).
remove_dups([X], [X]).
remove_dups([X,X|T], R) :-
    skip(X, T, WithoutX),
    remove_dups(WithoutX, R).
remove_dups([X,Y|T], [X|R]) :-
    X \= Y,
    remove_dups([Y|T], R).
 
process:-
	remove_dups([1,1,2,2,3,4,5,5,6], T),
	write(T),
	true.
 
:- main.

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