neg(~X,X).
check_neg(~A).
get_vars_from_clause([],List,List).

get_vars_from_clause([H|T],List) :-
    get_vars_from_clause([H|T],[],List).


get_vars_from_clause([H|T], T1, Acc) :-
    H = [],
    get_vars_from_clause(T, T1, Acc),
    !.

get_vars_from_clause([H|T], T1, Acc) :-
    not(check_neg(H)),
    not(member(H,T1)),
    get_vars_from_clause(T, [H|T1], Acc),
    !.

get_vars_from_clause([H|T], T1, Acc) :-
    check_neg(H),
    not(member(H,T1)),
    neg(H,H1),
    get_vars_from_clause(T, [H1|T1], Acc),
    !.

get_vars_from_list([],[]).
get_vars_from_list([H|T],List) :-
    get_vars_from_clause(H, List1),
    get_vars_from_list(T, List2), append(List2,List1,List).